I'm only 51 and I'm happily married, but here's what I'm thinking for lines:

"Older gentleman with his own teeth and an active mind seeks bright, witty companion for book discussions, movies, quiet nights in, a few nights out and hanky panky as bodies allow."

or

"Respectful retired professor seeks bright, caring woman. I like the occasional glass of wine, a good home cooked meal and peace and quiet."

or my favourite:

"I'm old, I'm lonely, I don't look like Brad Pitt because even Brad Pitt doesn't look like Brad Pitt anymore. If you're looking for honesty, companionship and the odd good time, I'm your fella."