Honestly, there's not a single verse that even speaks of the age of accountability. From the principles throughout many scriptures which speak of personal responsibility, free will and choice; the age of accountability is most likely when that person comes to a certain level of spiritual awareness.

The age of accountability is one of many misleading terms which are often used in Christian circles. Most people would agree that basically it means, 'a person who is young enough that he is not yet able to understand fully the results of his actions' (It being theorized by some that these children are not held accountable for the things which they do which are against God's law). For example, a six year old child that might hit his sister over the head with a toy block in nger. 'Theoretically,' this child is not held accountable by God because he had not yet reached an age where he is able to fully understand what he was doing. The problem with this theory is that it is based upon the logical processes of fallen human thought, and is a perverse twisting of God's law for the sake of what seems right in our own eyes. There is nothing in God's law that says man must fully understand sin, before it is actually sin. On the contrary, this doctrine is both un-biblical and self serving, for it presupposes unrighteously that sin must first be recognized as sin before it is actually accountable. Nothing in scripture supports such a thesis. Another theory is that all children are automatically guaranteed Salvation because God loves children. The texts most often quoted are verses such as Matthew 19:19, Mark 10:14 or Luke 18:16, where Jesus says things like "Suffer little children, and forbid them not, to come unto me: for of such is the kingdom of heaven." But this is a misunderstanding of application, for here Jesus is using Children as an illustration of the Christian as he is a child of God. He is making the analogy of how the believers are to be humble 'as children.' The teaching is that they are to walk meekly, accepting and receiving the Word of their father as Children do with their earthly fathers. This has nothing to do with Children being righteous or without sin, which is actually a heretical teaching. For all professing Christians should know inherently that 'there are none who are without sin, except God,' and only the elect, those washed in the blood of the Lamb, are automatically guaranteed Salvation. While these doctrines of accountability may serve to comfort bereaved parents who have lost children either through accidents, murder, miscarriage, abortion, or sickness, it is not a Biblically validated view, and is contrary to all that God has declared of sin and those who commit it. The plain truth is, this is simply a natural humanistic response in sentimentality related to man thinking more of himself than is justified. i.e., we naturally all want to think nice things about children. But man does not govern how we are to understand God's Word, the Word itself should. And God doesn't share the popular Church opinion that children's sins are unaccountable because of their age. Proverbs 20:11 "Even a Child is known by his doings, whether his work be pure, and whether it be right." This is just one of the scriptures that knocks down any concept of children's works being pure because of an age of accountability. The fact that this verse says implicitly that a Child's doing can be impure, is a testimony in itself against the doctrine of Children being sinless. They can't be known by their doings if all children's works are pure. They obviously are not all pure in God's eyes. More on this link http://members.aol.com/twarren13/account.html

I think different people reach it at different ages specaily mental handicap people

There's no verse in the Bible that mentions an "age of accountability" per se, and nothing in the New Testament that touches on it at all. Now if by it one means really "the age of full culpability for their wrong actions," the only indication is in the book of Numbers, which sets it at 21. Specifically, because of their disobedience and faithlessness, all the Israelites over 20 (except Caleb and Joshua who believed and obeyed) were condemned to spend the rest of their lives wandering in the wilderness and never enter the Promised Land.