To tie the knot at an early age isn't an insurance of enduring love and affection. I personally watch my friends getting married pretty early and make my own conclusions.
You change so much during your 20s, so when you wait until your late 20s, you've faced those growing pains, and they don't burden your marriage anymore.
Also when you make a commitment in your early 20s, you don't know what you want in a partner. You marry just because he/she is. It often comes through having an active dating life that you come to know the type of person who brings out the best in you. As a result, by late 20s, you have a better sense of what you'll compromise on in a partner and what you won't.
If you want to make a good career early marriage is only an anchor in this case. You'll have to consider your partner's needs and not yours only. You won't be able to be aggressive because you're married and this sense is just moderated.
Plus when you don't get married in your early 20s you have time