"Never, I'll still play the same games no matter how old I manage to get"
While it's possible gaming may not always be a part of my life, I find it highly unlikely. People that like watching baseball like watching it their whole life. People that enjoy movies will do so until the day they pass. Why would games be any different?
Now, if I end up with bad arthritis in my hands or something that makes it painful/impossible to play, then that would obviously change my answer. But, assuming I stay relatively healthy into my later years, I imagine I'll continue to play video games. Heck, even my grandmother plays games (albeit mobile games) and she'll be 90 this December.