What's wrong that? When anda have a crush on someone it really doesn't matter what age he atau she. There's lots of people who have a crush on a older man atau woman and a young man atau woman. So there's nothing wrong if anda have a crush who is younger
It's natural that u have a crush on someone younger it doesn't really matter what age he atau she is just tell him if ur ready maybe honesty will make him have a crush on u too