Jeb's problem is that if a Republican wins in 2008 he wouldn't be able to go in 2012 most likely.
That's not a problem, insofar as age goes. He's only 51. So in 2012, he'd still be only 59. He's young enough that he could even run in 2016, at age 63.
So what? He's about 8 years younger than W. If he's really interested, he could run in 2016.