In the bible you will find in the gospels many instances where Jesus knew their thoughts and in Acts where Paul discerned when he was brought before the council that half were Sadducees and half were Pharisees and played them off on each other. In the Gospels, Jesus never healed any two people the same way. The reason is that no two people are the same and He met their needs accordingly. Take the gift of tongues for example, it was given to different people for different reasons. Same with prophesy! Check out the books of the Prophets and note that no two received prophesy the same way! So it isn't hard to understand how the gift of discernment will also be different from one person to the next. As far as the age is concern, Samuel received his gift at an early age and it was demonstrated many times as he was growing up. Samson received his before he was even born and with many demonstrations as he was growing up. Jesus when He was 12 was in the Temple arguing with the scribes and priests astonishing them with his understanding. Now the only thing is that if by the gift you see something concerning somebody and you don't warn them then God will hold you accountable. Check out the Old Testament when prophets didn't do what they are suppose to. One example is Jonah being swallowed by a whale. Luke 12:48 "But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more. " Of course remind your father this about gifts apply to all who have them. Mark 6:4 "But Jesus said unto them, A prophet is not without honour, but in his own country, and among his own kin, and in his own house. " If he wants more detail; I can give him more detail. I learned this from a Pastor who also was a prophet who, among other things, prophesied about the Challenger blowing up 2 weeks in advanced including the headlines would be in both my hometown newspapers would be and the political cartoon would be on the opinion page in those papers.