Gin
Bet your mum's happy you're having a long engagement 
Tbh being practical, it's less of a life changing, irreversible mistake to marry the wrong man in haste in Vegas at 20 than to have a baby with the wrong man ...
Some people marry young and are married 60 years. I was 5 years older when I met DH but we moved in together within 6 months which many would say is too fast (didn't marry for another 4 years though).
It's the idea that you are viewing your role in the relationship passively Liley that is more worrying than your age or relationship length.
Don't be flattered that he wants to marry you and just go along with it if he's taking you for granted! He should be as flattered that you'd want to marry him as you are that he proposes. He should not assume that you will marry him this year if he hasn't asked you. You should be calling the shots as much as he is.
Otherwise there is going to be a big power imbalance in your relationship, and you won't be equal. If you don't want to buy a pub, if you want to save instead of take 3 holidays, if you want to TTC or you don't want to, if you want to live in another town or he does and you don't, if he wants his brother to move in with you following a break up and you don't, or you want your mum or sister to and he doesn't... you need to know you have truly equal say.