Just wanted to say hi as your thread popped up in active and I am not pg but I did have my dd when I was 23 (so pregnancy was 22) and whilst I didn't feel young as such I know exactly what you mean about feeling excluded from the other mums at the time.
For instance I had my own place and everything but I was renting and it felt like everyone else I met (though baby classes / pregnancy exercise class) were in such a different league with their massive mortgaged houses and professional double income households.
From someone 10 yrs down the line, I want to tell you that all will be fine!
You will be the absolute envy at the junior school gate when the penny drops that when my kid is 18 I will only be 41 (ha!) and also, if anyone and I mean anyone makes you feel less than worthy because of your age and what you have/don't have then please sack them off straight away and go talk to someone else.
I could have saved myself a lot of heartache trying to fit in with people who just weren't...... Nice, in any way.
I don't think that was necessarily an age thing, or an income/job thing, they were just bitches.
So watch out for that.
Truth is, you'll have a great time being a 'younger' mum. It's only recently that it is more unusual to have babies at that age. It is purely societal change as women are more likely to have careers now. Remember biologically you are COMPLETELY normal!