With the advent of Crossfit and other programs designed to develop all around functional ability, there are far less young guys getting involved in bodybuilding. Many gyms in fact are discouraging bodybuilding altogether. We have guys in their 40's dominating the Arnold. I fear for the future of our sport. How come young guys aren't getting into this lifestyle anymore?
Bodybuilding is just fine. Shows like the Nationals and USA have posted record amounts of competitors in bodybuilding.
Many "gyms" are anything but. They're built for resolutionist-types, who'll be gone in 3 months or so. Why do you think they keep advertising "No committment"?
A lot of the young bodybuilders are taking time off, between their winning a pro-qualifying show and actually competing.
As for guys in their 40s dominating, that's because they are learning how to stay competitive longer. Dexter Jackson is a prime example. He once thought he was fading into the sunset. But, now, he's revived and almost better than ever. Many have claimed that he looked better at the Masters Olympia than he did, when he won the real Olympia.
There are more supplement and magazine contracts. That also helps older bodybuilders stay in the game longer.