Mark. Congratulations on your first marathon and for having the balls to do it when you're 60.
Tiredness afterwards is fairly normal and a lot of books would suggest that you only do one or two per year due to the stress it puts on your body. I think that we become very complacent about how hard marathons are on your body.
How long you'll take to recover will probably depend upon how well prepared you were and your general fitness going into it (no disrespect meant). Had you followed a proper plan and done all of the long runs ? Did you suffer more than you expected during the run ?
I'm still suffering after my last marathon 4 weeks ago, which was my 8'th in about 3 years, but I didn't feel well prepared going into it. I'd ran another marathon 6 weeks before where I'd got a PB by 4 minutes and felt great the next day.
I'd suggest that you either just rest until you start to feel better or go and see a doctor to get your bloods checked.