Fun fact: I got a very stubborn and aggressive yeast infection a few years ago from some grimy motherfucker in the gym that probably never washed his junk and DEFINITELY never wiped down after using the machines. I couldn't have sex for a long time after that and NOTHING could get rid of it. Pissed me off so fucking much. Eventually my body completely rejected the infection and peeled off everything there and finally I'm infection free.
The gym is dirty, but it's a good place to meet women and to use up your energy. Always bathe afterwards. Acne is also caused by hormonal changes within your body (steroid use or natural changes) NOT only by greasy skin - it's perfectly normal at 20 and I finally stopped getting fucking pimples all the time at around 22-23. It's by no means limited to the teenage years exclusively.