There should be no age limit for this. Minors (without independent capacity) can go with adults. If you exercise your muscles, do some strength exercises, both upper limbs and waist and abdomen. However, for strength exercises of lower limbs, I feel that I can do sitting posture. As for the lower limb standing strength equipment such as Smith machine, it is better to do less. After all, it is still in the stage of growing up, so don't put too much pressure on your spine.