I feel like I had my "mid-life crisis" when I was in my late-teens and early twenties. Becoming an adult (in other people's eyes, at least) crushed me, as I was totally unprepared for it. The crisis resulted in very severe mental health problems and alcoholism. Pulling myself out of those things was not easy, and took me well over a decade, and there are still occasional lapses.
Approaching middle-age, in my mid-forties, I had almost the opposite of a crisis. I discovered my autism, was officially diagnosed, and began understanding myself much better than ever before. Using that knowledge to improve my life has been difficult and frustrating at times, and there's been the occasional crisis, but overall, it has so far led to a steady, gradual, improvement in my well-being. The people around me might not see it that way when they compare me to themselves, some even see my greater expression of autistic behaviours as signs that I'm "getting worse". So long as I feel greater satisfaction and no-one feels that I'm hurting them, I just ignore this; it's not their place to judge what does or does not make me feel better. Thankfully, the people who I care about most accept this.
Conversations where people idealise and reminisce about their wonderful youth mystify me. I wouldn't turn the clock back for all the tea in China, even if I could do it knowing what I know now; I have no wish to relive the kind of social pressures which society places on people at that age. I've just started playing with Lego again after a break of nearly 30 years, and I'm loving it; it helps me to relax so much. Am I being childish? I don't know and I don't care; it is no more pointless or vacuous than many of the things that the "adults" around me seem to enjoy. Have I missed "milestones". Yes, I certainly have, but I realise now that I only wanted most of them in order to "fit in", not because I had any genuine desire for them or because they would feed my soul.
Physically, I'm deteriorating a bit as everybody does, but this is more than compensated for by getting closer to living the kind of life that I actually want to live. Mentally, I don't feel as if I'm any particular age at all, I just am who and what I am.
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When you are fighting an invisible monster, first throw a bucket of paint over it.