Flux capacitor.

ME: Yeah, lately I’ve been feeling my age.

HE: Oh, you’re starting to get some aches and pains?

ME: Nah, physically I feel great.  Best I’ve ever been.

HE: Then you’re starting to forget things?

ME: I’ve always forgotten things.  Now is no different.

HE: Then why do you feel your age?

ME: Because I realized that in a few years, if you were to travel back in time and attend the world premiere of Back to the Future, you’d be traversing the same span of years that Marty McFly did when he visited his parents in the ‘50s.

HE: ...

ME: My ‘80s is like the ‘50s to the kids of today, see.

HE: ....

ME: ....

HE: ...maybe you should be very selective about the people you make that analogy to.

ME: I know!  I don’t want to just randomly depress people.