I'm definitely not an "older" member, I'm probably median age on here, but the closer I get to being in my 30s, the grumpier I get too, lol.
I think some of it is that when you get older you develop more of an understanding of what's going on around you, and in your own life, and you kind of lose the rose-colored glasses a bit. Especially if you've been through traumatic experiences.
I used to be overwhelmingly optimistic, but a lot of things that have happened in the past six months or so, in my personal life and also on a global scale, have kind of zapped my positivity. Plus constantly dealing with people in various aspects of my life who are always combative and angry. I broke down and lost the energy to deal with it after a while, so I lost my filter a bit in general and have more of an attitude.
I haven't noticed worsening of autism symptoms particularly in myself, other than having less of a filter when something annoys me, but being more grumpy, jaded, and disgruntled... definitely.
Part of why I'm distancing myself from serious threads, at least indefinitely, is that I need to get professional help for the depressive episode I'm going through, and some threads are so triggering that I really need to stay away from them. I don't really count this as a "serious" thread but I thought my experience with this may be helpful for you. Sorry if it isn't and this was just a ramble, lol