I am in my late forties. Last year, I was passed up for a seat on an executive committee, because the nominating and selection committee thought I was 'too young'. They did not ask for birthday information, and had they hung out with me for any length of time, they would have heard some of my 'war stories' from my military time. But I laughed my socks off when they told me they thought I was in my late twenties. Ageism in reverse! (I will probably get the seat this year. They've learned their lesson!)
People rarely guess my actual age- they tend to be a decade off, or more. They think my younger sister is older than me (she hates that!), and I got carded on my 40th birthday. While I've 'gracefully surrendered' the (sillier) things of youth (like riding roller coasters, sad to say- back and neck injury), I still dress like a younger person, preferring jeans and T-shirts to 'fogie-clothes' of my elders. You'll never catch me wearing a polyester twinset with pearls- I -hate- polyester with the fire of a thousand suns.
While it is nice to be young-looking, it does make my professional life difficult. My refusal (due to sensory issues) to wear certain kinds of 'corporate drag' has kept me out of certain jobs, and I have a difficult time getting men to listen to me- until I pull rank on them, or do one of my cyber-necromancy miracles. People don't believe me when I tell them that I was 'present at the beginning' of the Internet, when it was still Arpanet, and we had to go to the comm center to get email. Or that I used to be able to read ASCII code off paper tape. I have to constantly prove myself to newcomers, although my seniority in my present job, and my hard-won reputation as an excellent tech have made that battle go away. But every time we get a new crop of people in our organization, I have to go through it with the guys.
It's an odd place to be in- a young face in an ageing body with "Beginner's Mind". But that is the hand I've been dealt, and I am trying to deal with it with as much grace and aplomb as possible.