Is it healthy to lose 15 lbs in 3 weeks?

I became fairly active person and ate healthy and I am 15 years old. Is this normal? Will I be skinny when I grow older and continue this? Or do you think I will gain weight?

I lost 15 lbs and gained muscle mass as I went on. I now weigh ~120-125 lbs.

Lose Weight As You Get Older - Ezine Articles

Recommanded Answer:
Wow well done! This is good, but not really normal. I ask that you do not starve yourself because that is very unhealthy but get all your necessary food groups everyday and drink mostly water. Exercise is key as well because you sweat all the oil and other garbage that gets in. I am expecting when you reach around 30 you will start to gain more weight. This is normal because you really do not need to please anyone with your body and at this time you will get bore of working out.