While I don't exactly hide the fact that I'm in my late 40s, I do find myself avoiding some discussions at work that would show my age, like talking about my older experiences or making pop culture references from the '80s or '90s.
Yes, you can talk about making yourself so useful that age doesn't matter, etc., but the truth is that age discrimination is often an unconscious bias, and I just find it easier to "pass" as younger than to spend my energy trying to overcome it.
Of course I focus mostly on just being good at what I do. There are benefits to age. Experience and knowledge, of course, but hopefully also wisdom and temperament.
If there's one thing I'd like people to take away from this thread, particularly people in their 20s, it's to re-examine your unconscious biases about age. How often have you assumed something about a person because they were older than you, and what can you do to overcome that and judge them on their merits instead?