It's not that you're still growing at 21. You are as tall as you will be. It's that your entire body has not finished what it needs to do as far as reproductive system, endocrine system, nervous system. That's all still growing bro. Your natural test levels are high as shit right now. 25 yr old is or was the "prime" for guys, so right now your test levels are higher than mine are naturally because I'm 36 and past my prime. I don't know a lot. I do read a lot of bro shit on here and I do a little research of my own. When you introduce testosterone into your body from an outside source(AAS) your body quits producing it's natural testosterone or at the very least it suppresses it. PCT is to restart that natural process. At 21, I hate to see you suppress and restart. My PCT is always the same man. It works for me, it's not perfect, but it's easy and I know what to expect. Clomid run for 4 weeks. 50mg/day for 14 days. 25mg/day for 14 days. I start my PCT on day 21 of my last injection of test cyp. Depending on what other drugs I've used, it varies according to their half life. Like this cycle I finished yesterday, I used test prop for the last 3 weeks of it while the tren ran out of my system. Now I wait 3 days from my last pin( yesterday) before I start my Clomid. 3 days because prop is fast acting and short duration with very short half life. Anyways, you have a lot to learn before your first pin man. Take a couple months or years and learn exactly what this stuff does to your body. It's not all great. Some things are terrible. Or can be terrible. And dude, one last thing. Everyone I know says they are" just gonna run one cycle." Shit, I said it, and then my expectations weren't met from the first cycle because I didn't know enough about diet, training on cycle and I had unreal ideas about what steroids could give me.. I didn't get what I wanted from it, but I did get a ton.. just didn't get me to superman status after i weeks..haha!. so, be realistic. Be patient. Be willing to research, learn, and take advice. In the gym, online, and in the information others have learned and studied.