Please bear with me as I have been writing this over the course of the evening, so I may have x-posted quite a bit.
I know people on here seem quite "anti-men" or that they are putting him down because of his age - I thought the same thing when I first started posting here, but after being here for over 2 years I have found the ladies on the relationships board to be very very wise. Especially (sadly) when they are telling you what you don't want to hear. Every time they have predicted something I've seen it come true. One thing I have learned is don't hang around waiting for someone to change, because they might not. If you're not at the same stage now, you can't hang on for ever in the hope they will be soon. Fair enough give it time, but don't wait too long.
FWIW I am the same age as you. I also had broody feelings since I was about 12, my sensible side said wait until you're in a stable relationship, wait until you have a good job, get some experience of life first, wait until you are in a better financial position etc etc. However I was never really careful with contraception. I was on the pill but used to miss them quite often etc. In hindsight I'm lucky I didn't get pregnant then.
Anyway then at 18 I met my DP, he was amazing, really romantic, actually wanted to be committed to me which I was completely over the moon about because it was a big issue I had with most of my exes. Within 6 months (I was now 19) we'd moved in together, things were great, I was really happy. One of the things I liked was being able to talk about the future with him, things like marriage, children, planning our lives together. I was getting fed up with hormonal contraception as well and made a decision (with DP) to come off the pill and start charting my temperature to do natural family planning. The plan was we would use condoms until I felt really confident with it. We knew it wasn't as reliable as other methods but both of us felt an accidental pregnancy wouldn't be the end of the world (though ideally it would be better if we waited). I did also consider the possibility that I might get pregnant and find he changed his mind and I ended up bringing the child up alone. I felt ok with this - of course it wasn't what I wanted but I knew if it came to it that I could. My mum brought me and my sister up alone and we turned out OK :)
Anyway, so we started using condoms. Just badly. It started off that we'd use them properly but both complan about how much we hated them, then we went to starting off without and then put one on, progressed to starting off without and him 'finishing' elsewhere, which of course included the occasional "oops" which I pretended to be cross about but didn't really mind too much (or I would have been more forceful in insisting on condom use, yes?)
I used to think about babies a lot, do a lot of reading of parenting sites, etc, and DP knew this and one day with the shopping we bought a "pregnancy and birth" magazine, just for a laugh, just to read. Went to check out the condom aisle and DP put a pregnancy test in the trolley. I was a bit 
as we hadn't any reason to think I might be pregnant. We'd had a scare about a week before but when I tested, it was negative. So went out and got drunk that night. The next morning DP got me to do the test. This is really stupid because of the unprotected sex we'd been having but I never in a million years thought it was going to be positive and it was a huge shock for me when it was. THAT was confusing in itself because all that had been occupying my mind for years was a fascination with being pregnant and babies and childcare and everything. Whenever I'd done a pregnancy test in the past mixed in with the relief I had always felt a slight disappointment. But now I was pregnant, the overriding emotion was fear. I didn't expect that at all.
Evidently because of the way I felt, abortion/adoption was never an option. Pregnancy = having the baby. It was scary because it had all been in theory before and now it was real, it was very scary telling family and friends, especially family I knew wouldn't be happy about it. The actual pregnancy/labour/babycare/childcare bit didn't scare me half as much.
So evidently I went ahead with the pregnancy. It was as wonderful as I'd always imagined - I didn't have any major problems etc. I loved feeling the baby inside me and I loved being pregnant. Most people were supportive and it was actually quite a happy time, though my relationship with DP was having some minor issues, mainly him not being as mature as I'd hoped. But things went up as well as down at various points and I thought well, we have to work at it, for the baby. And I expect he'll grow up quickly when the baby arrives. The issues he has are mainly maturity issues. He knows he has to grow up and having a baby to care for will help this along.
But still, I had doubts. I wondered a lot if I was doing the right thing. Some of the minor niggles were less minor than I was admitting to myself. I cried myself to sleep on the night DS was due thinking I'm so sorry baby, why did I choose this person to be your Daddy?
Had DS. (I was now 20) Loved the labour. Loved the birth. (DP was brilliant during labour BTW, oh, except the part where he took me to burger king 20 miles away and left me contracting in the car park but the actual birth he was good). Loved having a newborn. DS was wonderful and it was everything I'd imagined, again, but still within a few days I was having problems with DP. He was out constantly "working" though he was supposedly on paternity leave. I had to cajole him hugely into changing a nappy. I was breastfeeding so he couldn't help with feeding but a few months later when I expressed so he could give a bottle he did it once and then didn't seem bothered. Basically he loved the idea of having a child as long as I did all the care, and DS never bothered him. He didn't grow up. Or stop drinking. Things just carried on as they were.
I have never regretted having DS - he kept me going through what started to become a very lonely and unhappy time. My friends were out drinking etc, which I couldn't do, because it's not as easy as just getting a babysitter - you have to factor in the cost, and whether your baby will settle for someone else (not just an issue for BF babies) and whether you actually want to leave them, and DP never wanted to babysit - so I lost touch with that group of friends. I had DP's friends who would come over in the evenings and I enjoyed their company, but sometimes they were just drunk and irritating when I was trying to get DS settled. I made a few new mum friends but we didn't have the shared friendship history so I couldn't talk to them as easily.
After about a year I just had enough and I left DP - so from now referred to as XP. (That feels better 
) So I was a single mum as I had considered, and it was okay - again, pretty much as I'd imagined. DS is funny, cute and incredible, and I'm glad I have him. Caring for him alone isn't too hard (as I was basically doing it anyway) but there are things which are hard. Although XP was gutted when we split, 15 months on he only sees DS about once every 3 or 4 weekends - we arranged that it would be every weekend. It's hard seeing DS love his father so unconditionally and getting a half relationship in return. It's heart-wrenching to know that XP exposes him to attitudes and things I'd really rather he didn't encounter at this age. It's shit now seeing the parallels between XP and my own father and knowing I can't stop DS taking from that the same messages I did.
It's also hard having him young - seeing friends etc starting out in careers and not being able to do that (I just started part time at uni this year :)). Seeing mum friends who are older in supportive relationships with their children's fathers and being sad DS couldn't have that. Wanting to be able to get DS things without worrying about money. Wanting to be able to go out and not being able to do that (FWIW I never ever thought this would bother me but at times it really, REALLY does.) Things like friends mentioning week-long holidays which wouldn't be the same with DS, or weekend trips, or festivals. Feeling shit that DS won't have a sibling close in age because although I was lucky enough to meet someone lovely less than a year from the split, I want to wait until the relationship is a LOT more established before thinking about children. (Although actually he does have a half sibling because XP got someone else pregnant 4 months after we split). Relationships are ridiculously more complicated with a child involved too.
I do look at DS some days and think I fucked up, not with him, because I think we're doing fine and I am proud of him, but just - all the things that are fantastic and wonderful and amazing about him, would be equally so if I'd waited and had children later. I still would have loved pregnancy and birth and babyhood and toddlerhood and be looking forward to the other stages - the difference would be I'd have a partner there who would really support me. Not just insist he was supportive because it meant we could have sex without a condom :( Someone who was as excited and enthusiastic about the baby as me, someone who would look after DS if I wanted to go out, someone to share the hard days with, someone who I know I can rely on because it just wouldn't be in his nature to be unreliable, or unsupportive, not just hoping all these things would happen. And it would be better for DS as well - I'm not fantastic with him when I am stressed which OK isn't all the time, but it's HARD! Not all the patronising things like "Oh you know you won't be able to go out and you'll be skint and the baby will cry a lot and they are a lot of work you know! And you'll get no sleep and it wrecks your body." - I knew all that and it didn't put me off and I still don't find that the hardest thing. It's hard emotionally. It's hard knowing you aren't giving your child the best you could have if you'd made a different decision.