On top of what TG Karnonnos said, excessive masturbation decreases testosterone levels in men, and increases prolactin. If you know what these are, you really don't want to do that. Unhealthy lifestyles pushed today and romanticised already do a lot of damage to men's testosterone levels.
A healthy level of testosterone, contrary to what sickness medicine of the enemy says, is 1000 ng/dL and upwards. Any lower than that is one of the leading reason many men nowadays are sissified lacking drive, motivation, focus, initiative, confidence, and optimal executive functions. Low testosterone also prevents many from having strong opinions, standing by their "guns", having healthy body (a healthy human body = what Greek statues depict, no other nonsense that people have in their hands nowadays).
It also creates hangups with your masculinity, and is a big obstacle in building true brotherly bonds with other men in your life, which is something that's supposed to be natural and automatic, as the nature of masculinity is not only to hunt for love partners but also have some sort of pack (i.e. like wolves).
Yang is extroverted, outgoing, intense. It's not surface-level garbage. It's also not worrying other people will think you're effeminate if you do X, Y, or Z. Yang energy is expressed/projected externally, meaning in society, community, in building something outside yourself. Differently from yin energy that's internal to develop yourself. How you express it of course depends on your specific chart, but it comes from a place of faith in yourself. The less testosterone, the more pacified and passive you'll be, which is very detrimental. Think of the Sun: the Sun gives life to everything. It's vitality. Or Jupiter. Jupiter expands outwardly. Mars's symbol is literally the Sun cross with an arrow indicating upward and forward motion, which is why Mars represents where energies are directed.
I could go on how detrimental low testosterone is for a man. The effects I described are just scratching the surface.
So, yes excessive masturbation harms your health. Everything excessive and everything defective harms your health, which is why a wise man once said that virtue lies in the middle.
Read about Temperance here:
https://templeofzeus.org/Apollo_virtue_6.php