Low levels of testosterone in young guys isn't just an event. There is a cause behind it and it can be important to determine what it is. Unfortunately, that can be a complex hit-or-miss proposition. In the case that the testes are just not up to the job, supplementation/replacement is important.
In my case, my T levels dropped below 300 quite rapidly quite a number of years ago. This coincided with me developing a whole set of seemingly unrelated problems. I went on injections of tesosterone cypionate and they helped with libido and energy but not the other stuff. Twelve, yes twelve, years later I was diagnosed with chonic Lyme disease. Getting treated with long-term antibiotics cleared up most of my other diagnoses (asthma, arthritis, BPH, apnea, "vertigo of unkown etiology," apthous ulcers, angular stomatitis, chronic fatigue, night sweats, disorientation.....). I was a MESS and now am basically well other than still taking maintenance antibiotics.
We decided to take me off T and try hCG to see if we could jump-start my pituitary gland, which sends a chemical signal to the testes to produce stestostrone and sperm. It worked in that it got my T level up but it would not stay up if I went off the hCG. What this suggests is that the Lyme disease affected my pituitary gland. We made a decision for me to stay on HCG, as everything just seems to be better on it, rather than T. Interestingly, switching to hCG brought my PSA down to 1.
I have posted on a website called lymenet.org for a number of years and my anecdotal observation is that almost all male lymies have low testosterone, be they sixeen or sixty, and almost all (again, young or old)have had problems with prostatitis.
So, externally introduced testosterone can definitely help guys who are already low. Among guys I have known, the injections seem to be more reliable than the gel. If possible, learning the underlying cause and treating it can have many benefits.
Dave