I haven’t been carded to prove I’m over 21 since… hmmm, well before I was 30, anyway. And that’s fine.
Not only have I not been carded for a senior discount (I’m only 63, people!), I get it automatically after they look at me! Or we ask for “one adult, one senior” ticket, and they hand the senior ticket to me instead of Deb (a lovely 67).
In my case I suspect it isn’t the years, it’s the miles. ¯\_(ツ)_/¯