Hi tiara,
If your bf is about your age, there are definately alot of things on his mind. He woudl have just left school,in his first job, hardly much savings in his bank account. Most guys take about 5,6 years to know what they really want in life. Getting married is not just tying the knot, as you realise. It's about deciding where to stay, what type of housing/car to buy, how to deal with both sets of parents, consider financial obligation. What happens if babies arrive after marrige. That will be additional expenditure. Would you and him be able to be role model parents?
I agree that a 2 years exclusive relationship pis enough time to know someone. But if the mentality is not "to know someone with a view to marriage", but "to know someone to be a bf", your bf may not be prepared to commit now. My hb proposed to be when we had known each other for about 15 months...he didn't think he was too quick cos he was 28 then. We only opened a joint account about half a year after he proposed.