While I don't think there is a certain age requirement. You probably should be 21, and must be for some work. Seeing as many DJ's are at clubs...which have Alcohol. Also, A basic knowledge of many instruments is most likely required. As is a basic knowledge of some computer systems. Seeing as most DJ's use computers to mix beats and songs.
I think you have to be at least 18. The stuff you need: a hooded sweatshirt that's way to big, headphones, a table with an innumerable amount of buttons, CDs, and records; the most popular songs, and a lot of people that want to listen to the music.