31 years old and they still want him probably because he'll come cheap. 

"It would figure to be a minimum deal worth $1.229 million."

"Collins, 31, averaged just 0.7 points and 0.4 rebounds in 24 games in 2009-10, his first season with Atlanta. But the Hawks like his locker-room presence, and his 7-foot, 255-pound frame provides plenty of size, if needed."

http://nba.fanhouse.com/2010/07/18/jason-collins-expected-to-re-sign-with-atlanta/