The guy who introduced to lucid dreaming just turned 57 (I believe) a few weeks ago. He still does LD but only about once every few months because he's not been actively engaged in it in years now.
I think age does affect one's LD ability but not in a way that can't be countered with conscious attention and working at it, like what we here at DV. It's common for natural LDers to be so at a young age then taper off or completely lose it as they grow to adulthood.

[mytheory] The focus of daily attention from play and fantasy to awareness of the external world and responsibility tends to make dreams more distant to us. As we become more a part of the external world the inner world gets squelched and muted. Children tend to be better at dream recall, or at least more aware of the dream world. But, generally speaking, as they learn to distinguish that dreams are not the real world*, the perceived importance of dreams lessens. [/mytheory]

In the very ways that we - as active** LDers - improve our odds of success, anyone with a sound mind (able to understand what 'dreams' are) of any age can have lucid dreams. I think a lot of it (especially for non-naturals) is about mindshare. Restore mindshare to childhood levels and you improve your odds of becoming lucid in the dream state. Even if that mindshare is on a subconscious level.



* Not necessarily in a lucid dream sense but rather, in terms of after the fact recollection.

** Active in the sense of intentional attention to (and mental occupation with) dreams during waking life.