Here are the two basic rules I propose:
Rule 1. Never mentioned your age to any cyclist young enough to be your offspring. Age may be discussed only with your contemporaries. Telling a younger person your age sounds like old codger boasting (pitiful) or asking to be cut some slack (really pitiful).
Rule 2. If asked how old you are by any cyclist young enough to be your offspring, respond with a crisp one liner. It doesn't have to be very clever. "A little younger than dirt," always works for me. Just say it with a big smile and move on.
Age is not a safe subject for social conversation. It's a mine field. Why venture there? Just remember that every younger cyclists wants, when they get to be our advanced age, to be riding around like us. Be content with that.
When I'm out with a group, it's pretty easy for them to figure out my general age. I've got the wrinkles, the age spots, and the sags that match their mom's or grand-mom's.