I was just talking about this at the Toronto meet-up last night, but whenever I meet someone I can have an adult conversation with, then I find out that they're younger than my little brother, so: adults that are younger than him make me feel old.
My
youngest brother is 14 now and in a few years, he'll be an adult and I'll be 30. Now I know that's not
old (which I consider to be about
Charlatan's age 
...well maybe old is more like 70 or higher), but it makes me reflect on my age.
Also, when I watch the Oscars, seeing certain entertainers on the deathlist (is that what it's called?). That makes me feel old.