When should i start to work out?

Workouts: 13 is a good time to start working out. You are still growing so you will get bigger and stronger without doing anything. I would recommend finding a mentor who is an adult and ask to join him or her in their workout. It's always more fun and safer working out with a partner. 3 days a week is plenty. At your age learn the proper lifting technique. Don't be concerned about the amount of weight.

Now: As long as u don't have any medical problems.