AJ McLean Turns 40, Looks Forward to First Prostate Exam

AJ McLean isn't even trying to hide it ... he's totally looking forward to getting his very first prostate exam, now that he's hit the big 4-OHHHH!

We got the Backstreet Boys singer Tuesday -- the day he actually crossed over -- and asked if he'd scheduled his first, y'know ... oil check, now that he's a man of a certain age.

AJ knows he needs to get it done -- probably sooner than later, it sounds like -- but the good news is he's excited about who's conducting the examination. He also reassured us his wife's on-board with another woman getting up in his business.