which steroid should a 18 year old use for normal body not huge?

18-year-olds should not use any steroids. As their bodies are still developing, all manner of damage can occur.

In fact, no one should steroids unless they are prescribed by a doctor for a medical condition.

I agree with the other responder. Steroids should not be used for building muscle. AT ALL. The consequences outweigh the benefits by far. If you're having a hard time developing muscle, look to your training methods and your diet. Don't take the short cut. Steroid abuse can cause irreversible liver damage, peliosis hepatitis, heart attack or stroke among many other things. Find a trainer and go at it naturally.

-Coach Albert

When you're 18 you really don't need steroids because at that age your body is producing so much testosterone already. Just get a decent workout plan, do it consistently and you'll start to get into really great shape quickly.