Well, the first thing that makes me feel old--I have attained an age by which most of my parents' generation had passed on (excepting my parents who lived until they're mid-eighties, and a couple of others.)

Second, I have far fewer years ahead of me than behind me.

Third, many of my generation have great-grandchildren, some of whom are teenagers.

Third, I remember my youth better than my fifties and sixties.

Fourth, I have more aches and pains, and less stamina than formerly.

To offset the psychology of aging, I speak of absolute dates (e.g. H.S. graduation in 1957, rather than 59 years ago.)

However the thing that absolutely makes me feel old: I can't go for a pizza at midnight after going to the movies...assuming that I could even stay up until midnight.