So I found this old post by Myates and it kind of eased my mind about DaBaDee (I'd rather him be old than sick from something nasty!)
Each betta will be different as they age, but typical signs of age is dulling/muting of the color (not to be confused with a sick betta who has become pale), so that the color isn't as bright as it once was. That can happen subtly, or quite significantly over time.
Also they tend to start getting a humpback.. in a sense can look like a salmon.
They can become "bony" in appearance.. and individual scales may look more prominent.
Loss of sight is quite common- not being able to see well, cataracts that look like a white film over the eyes. You can tell if losing sight by him lunging at food and missing, not noticing things outside the tank as often, etc.
Gradual slow in activities.. older bettas tend to lay around most of the day, whereas young ones should be quite active. But it is gradual, if it seems sudden then there is most likely something else going on with your guy.
Older bettas may not show the enthusiasm for food like they used to. They may show less interest in their humans or stop their “wiggle dances” entirely. Their tenacity for flaring may lessen over time as well. A betta that used to put on a show for other males or his own reflection may not display with the gusto he once did.
All of those signs should be gradual, to where you don't notice them happen "all of a sudden"... if one day he is fine, and the next he is showing these sort of signs then that means there is something else wrong with him that isn't age related.
He has ALL these symptoms. Dull color (kind of blue, still, but more brown, kind of transparentish, not white like when they are pale), humpback, bony, misses his food when he lunges, very lethargic, less frequent "wiggle dances", won't flare. And it definitely didn't happen overnight. I started noticing duller color a while ago, but I know it's gotten worse. I know he's gotten more lethargic. But it's been getting worse for months.
I'm just glad, that he isn't sick with something really bad that could affect my other fish... I just don't know why he's buoyant, even with Epsom salt...