1 or 2 times. If you rip your muscles it can damage your body PERMANENTLY!
Well im not 13 im 14 but i started going to the gym with my mum and dad almost every week day but only for cardio. If you want to tone up muscles though i think yoga is very effective to do a couple times a week
It depends on how much you weigh, if your on the heavy side, work out once or twice a week. If you are fit, you could work out three or four times a week.
You should only do stressful lifting two times per week and don't feel like you have to do lift a lot of weight. It is important to understand that you are still growing and should not try to over lift. Make sure that cardio takes up about 85% of your time in the gym.
Once every month your little