Frankh, its always nice to be head hunted. Makes you feel good inside.
Seriously though, what they said!
If you really want to retire, stop playing around, get off that site.
If you really want some part-time work, contact them and say only if its part-time. Personally I'd do that by email, so they know up front thats all you'll consider and its harder for them to schmoozle you, at least at first anyway.
If you are worried about losing your finely "honedness," could you find some other way of doing that outside the workforce? Are you worried about your brain turning to mush or loss of your specific knowledge/skills that might make you employable in the future? Different answers according to which it is.