HGH can be used at any age, Younger individuals will need higher doses to attain what someone older with lower doses would need. It all comes down to goals with the hormone. If you cant afford lots of it then muscle gain should be out of the question, but if fat loss and repair is what your looking for go ahead.
With muscle mass, doses of 10iu+ per day for long periods need to be used, most run less than half of that per day. 4iu Everyday for as long as you can run it, will bring a nice leanness to you, keep fat at bay while bulking, increase collagen synthesis and strengthen bone and joint health. Start with at least 4kits @ 4iu that is 100 days.