i would also suggest lowering the water level so it's easier for him to get some air. just keep feeding him a little each day or every other day. theres not much you can do if its old age, just let nature take its course.
Inactivity usually is a hint that he is not well... here's a very good site that lists the symptoms & treatments of betta diseases: http://www.bettatalk.com/betta_diseases.htm
Maybe he's bored... but if you give him a few days he should be exploring his new home.
HTH. keep us posted of how he's doing =)