I've said all this before but I want to talk about it again.
take the bw manga and it's clear grimsley is 35+ this isnt new info. he said he was a casino dealer for over a decade. unova is based off new york, which is in the US.
pokemon still tends to uphold the laws of the worlds they're based on, and according to US laws you have to be at least 21 to be a dealer in the US. You can go to dealer school at 18 the earliest, but can't work until you're 21.
By that logic, Grimsley is at least 31+ at the start of BW. 33+ in BW2. 35+ in Sun & Moon since it's stated in his concept art from his character designer that it's only been "two years" later.
Stress can cause premature greying. It happens to many. It can also age you drastically based on how much your body is trying to handle, especially if it's coping with trauma. It's why you can see major differences in people who've come back from war or other tragic events.
Anyway, to close this off, I am restating that since Alola is based on Hawai'i, it's worth noting that gambling is illegal there and I find it rather interesting they placed Grimsley there. Part of me will always believe that he is there for a purpose, and he states that in his own way (taking up surfing). I like the idea of him trying to rebuild his life and make sense of it, as one might do at that age.
