Yes, it is healthy and you will sleep better.
Masturbation should be done in a place where one has privacy. Favorite places are in the shower or in bed at night. If you masturbate in bed, then an old sock is useful for catching the ejaculate.
There is no lower or upper age limit for masturbation. Some pre-school boys masturbate and some elderly people masturbate at least into their late seventies.
One may masturbate as much or as little as one wishes, however one may experience temporary sexual exhaustion due to very frequent masturbation.
Three times a day works well for many teens.
1. Do it before school in the morning. This helps you get through the school day without being excessively h*rny.
2. Do it after school because you have gone a whole day without masturbating.
3. Do it before going to sleep. This helps with restful, sound sleep.
The movable, internally-lubricated, nerve-laden erogenous foreskin and its gliding action is an important aid to masturbation.