I don't think there is truly a right or wrong answer to this. The only right answer to whether or not two people should get married is when they are truly ready and mature enough to be married. Some people are more mature at 20 than some 30 year olds, and vice versa. A friend of mine is the same age as me (38), and his maturity level is more of a college kid. He's married, but her mentality is about the same so they happen to be perfect for each other. I am a much older 38 than he is. So putting a number to readiness is not the answer.
That all said, I married at age 33, and he is on his second marriage.