I was just 20 when I had my first (yes, she was a surprise, but the best one EVER!), so no stranger to the prejudice. Am now 16 weeks pregnant with my 2nd ... will be 36 when the one arrives. Have experienced remarks this time around such as "oooh, that must've been a shock??!! " Err, no, it was very much planned, thank you very much. Will be a 16 year gap between them, so - like Shiny - I will return in 10-15 years and tell you what I think!
Joking aside, in my opinion, age really doesn't matter. So, some 'older' parents might have higher earnings/paid off more of their mortgage/have more life experience/have more security blah blah blah when they're older, but only some. Not all. I really don't think that's what makes you a good parent. In my humble opinion, I have been a fabulous Mum to my DD (despite being so young, and being skint for several years after going back to Uni) and really can't see me being any different to this one.
Ignore any negativity, you are doing what is right for you, so enjoy! 