Doing an exercise video is usually cardiovascular exercise, which is always fantastic. If it's weight exercise, that's okay too, as long as you don't go too high with the weights. Five pounds sounds all right.
As always, no matter your age, if you hurt yourself during exercise, give your body a break until it heals. Otherwise, you should be fine.
I absolutely agree with BedsonTrudeau.
This myth, that working out, weight lifting and exercising can stunt growth is so wide spread that sometimes I can’t believe how little people know and how much boys are ashamed to ask the things they should ask.
First of all, I think it is great that you are working out because most of the guys in your age have something else as priority. Working out will help you to develop nicer and you will be in a good shape and the benefits of great body are probably very well known to you.
Be careful not to overreact and always consult with your trainer before increasing the weight you are lifting and be sure to drink a plenty of water while you are exercising.