I don't have any exogenous HGH to inject myself with -- however I have read that you can increase your natural HGH levels by up to 1250% just through fasting.

https://intensivedietarymanagement.com/fasting-and-growth-hormone-physiology-part-3/

By performing a 21 day fast I will raise my HGH levels and lower my insulin levels.

But is HGH the only thing that determines your height or will fasting stunt my chances of growing (if I have any more chances to grow)?

I'm not sure if my growth plates are closed.