One suggestion I used to use- if you feel yourself 'pumped' after a work out (normal), go into a bathroom stall and jack off to take the 'edge' off...

As an older guy I have seen a few hard ons at the gym... I take it as just what others said a normal reaction for a healthy young man...

Also- don't make eye contact...if you make it a 'big deal' and look embarrassed, etc... then that will only make it worse.

A (large) towell can also help to hide...esp if bosses are present. I think they would rather you shower than to 'stink' around the customers...