Great question - thank you!
So one age comment alone isn't going to be a hostile work environment -- but it is insensitive (and therefore a problem).
Here's a suggested response next time that happens:
"[name] - my age has nothing to do with my work performance. If you want to critique my skills or work performance -- that's fine, but please don't link it to my age."
Try to say it in a nice, polite way so the person doesn't react negatively to your attempt to change the situation.
Hope that helps.
Workplace Harassment Expert
February 9 2018