I started when I was 7, by my older cousin who was having trouble finding players at the time. While It hasnt always been D&D, I have been roleplaying/Game mastering for 25 years now.
And while I may not be activley playing at that age( that would depend on who there was to play with.) I would deffinatly be involved in it in some way, even if it's only coming here or some other board and lurking like the shameless hermit I am.
I deffinatly could see using your retirement to build the ultimate gaming house, complete with all the stuff you need for those extended campaigns. Whats that guys, you want to stop becuase you all need a nap? Take any one of the many guest rooms, all totally geeked out with everything you need to be comfortable. What your hungry? Raid my fridge or we can order out to one of the many different resteruants in the area. ( I wonder if I will still be able to eat Thai food at that age?)
Need someone to help change your sack? Your on your own there buddy, but I do have enough rooms for your nurse should you need her to stay.