Age

The other night I Was coming home from work when I recieved a text message from a cousin of mine. It said " Kristen you need to watch out for your younger cousin she is doing bad things." So after reading this I think she is involved with heavy drugs or cutting out of school. Turns out shes seeing a 26 year old( and she just turned 17.) Ok thats nine years. So eventually my older cousin called me and he was flipping that it is too big of an age difference. How come age only matters when you younger? What does a man who is that age want from a little girl? Perosnally I just think it is disgusting. But at what age does the difference in birth no longer matter? I have family members where the girl is about ten years younger than her husband. But seriously at the age 17 you should not have the same priorities as a 26 year old man. I totally understood where my cousin was coming from with forbidding the situation. But at what age does age just become a number?