I don't think it is age related, I would still do a water change to rule that out as part of the problem.
A good rule of thumb so-to-speak...anytime you have a behavior change-check the water temp and make a water changes even if you just did one earlier in the day or week.
To rule out environment at part of the problem-anything could have fallen in the tank, hands, sprays, oils etc.....and water temp is also very important to check.
How old is he and how long have you had him? how is his appetite, how big is the tank, water changes, additives, live plants, filtration..etc...
Often when a Betta has a change in behavior making a 50% water change can perk them up and this will also help rule out the environment as the problem.
Just ignore those people frogipoi, some people are set in their ways and believe their method is the only right way to do things.....and just because you have never had a spawn doesn't mean you can't post about it.
To grow and learn you have to open your mind and see the whole picture and understand that there are just as many right ways as wrong ways to do nearly everything.
I think your thread is a good one...so don't feel bad...those people are the ones missing out on the reason it was started......
keep your chin up....and ignore those people......
Doing great, little fry darting all over the place and the male tending nicely to the nest. Got to start adding some tap water to start getting them changed over to it in the next day or so and bring them in the house within the next month.