"How often is safe for a young guy? " They are not safe. My husband’s nephew had a membership in a tanning bed salon for a year. After it expired, he stopped, now he's as white as before he began (photo below).
25% of the sun damage (or tanning beds) occurs by age 18.
Tanning comes & go, unless you do them everyday 24/7 for the rest of your life. But in the end the only thing you'll benefit is either moles, freckles, skin tags or discolorations from sunscreens, lotions, etc. and the more you do, the more they get larger, darker & bumpier.
I'll let Lisa & Glenna tell you HOW SAFE:
In April 2005, while working out at her college gym in Rhode Island, 22-year-old Glenna Kohl detected a hard, golf ball-size lump near her groin. . . . .In high school, Glenna did have an irregular mole removed from her leg. A pathology report identified it as benign, but the surgeon tested it again. The lab had made an error: The mole was an early stage melanoma.
"Plastic Week: Lisa Gastineau On The Dangers Of Tanning Beds" She had 2-3 melanoma moles removed, one by her nose. She had nose surgery just to get her nose straighter, so she can breath again. She got those moles from a tanning bed.
Tanning beds aged you by 10-15 years! They are also worst than the sun.