The hormones you need to know
If you want to grow your penis, you need DHT gel, and maybe IGF1 which is not available. I don't know if these will actually grow your penis, but please read more. I will post links to studies soon, though they are easy to find with google.
To understand why your penis is not growing now, you must look at what is different between puberty and adult hood. I think the answer is which hormone modifying proteins and which hormone receptors are active in which tissues.
I spent a few years studying hair loss and how hormones affect it. I then stubbled on some penis studies. The two are interconnected.
DHT is manufactured in the tissues where it is used. It is not transported in the blood, but rather is quickly broken down in the blood. It is made by 5 alpha reductase types 1 and 2. Type 1 is in nerve cells and oil glands and maybe other tissues. Type 2 is in hair follicles, the penis, the prostate, other places, and maybe even the part of the brain that makes GABA.
As you get older, androgen receptors and 5 alpha reductase in your head hair and body hair become more active. Your head hair and body hair respond oppositely to DHT. DHT is the androgenic signal in most tissues except your muscles, which respond to just testosterone. Only the DHT made in your scalp affects hair loss. The DHT in the prostate is quickly broken down once it enters the blood.
Estrogen is good for scalp hair. Estrogen fluctuations cause reversible sheds. Estrogen strongly slows or reverses penis growth. When you inject with testosterone, some tissues with turn it to DHT, and to estrogen, in different proportions depending on the enzyme activities in those tissues. And the receptors will vary too. Extrogen in the penis often overpowers DHT. That is why testosterone gel would not grow your penis.
Growth hormone might grow your penis. Injecting a little into your penis with a 31g needed (do not use anything bigger) might be more affective. It depends if your penis has the enzyme to convert HGH into IGF1. It is actually IGF1 that does the growing. You can buy IGF1-LR3, but it might now work like IGF1. At least the effects are local since it can't bind to blood proteins. I don't think you can get IGF1 anywhere. Teenagers make up to 12 IU of HGH per day, though 6 IU might be average. Adults are 1-2IU near 25-30.
You have many HGH IGF1 conversion receptors throughout your body.
Testosterone topicals/injections can shrink your penis because it can be converted to estrogen in your penis. You want DHT.
6-oxo on your penis might help.
Proviron/Masteron last too long to have a local effect.
Natural DHT is quickly broken down in the blood.
Propecia stops the 5ar2 in your penis from making DHT.
After puberty, you make less DHT down there, and more on your head.