I was in your position, feelings wise, at 20....although still living with parents, we had been together for 2 years too. We did try because it was all I could think about and was taking over my life and like you was very maternal etc., I finally felt like I was getting over it and spoke to my DP and he felt the same about waiting until we had a house and I had finished my degree, little did I know I was already 8 weeks at this point.
I'm now 26 and 22 weeks preg with 2nd DS. I was exactly the same again, couldn't stop thinking about it, on forums everyday, even looking at baby clothes and how I would decorate a baby's room. My DP wanted to wait as we had a few debts we wanted to clear. I finally come round to the idea of waiting as I knew I couldn't change his mind anyway....again I was already 5 weeks at this point!
I would definitely say if you feel ready and so does your DP then you certainly aren't too young. My DS started school in September and he is a very much loved, happy, healthy and clever little boy. I wasn't one for going out anyway, I don't feel like I missed out on any of that. Both my DP and I work full time now, I carried on and got my degree (which helped me get my job) we bought our 3 bedroom house and we both drive and have cars. Having a baby young didn't stop us.
We had just booked a 3 week holiday to Cuba the day before I found out I was preg with DS1, I was 17 weeks by the time we went, I wouldn't say it ruined my holiday, the only thing that was different was that I wasn't drinking and was being careful about what I ate. We have still managed to travel quite a bit since.
I would talk to your DP and explain that you feel like its taking over your life and you don't want to wait any longer. That is if you don't mind being preg on holiday? He might not feel the same but you won't know until you speak to him.
Sorry went on a bit there didn't I!