What rugby boots does my son need? what position will he play?

Hi I have an 11 year old son about to start secondary school in september and have to buy his rugby boots, i have noticed there are different styles for different positions. Additionally, he has never played rugby before, although he is a very fast sprinter, he trains at athletics twice a week and currently sprints 60m in 8.7secs. he is very slim build and slightly below average height. Please help