I started cutting my own at 19 but it was basically just growing long. Once in awhile I would tame it it. I was cutting my wife's long straight hair of the era too. My hair is natural curly and definitely does not hang well long so I found a happy length that has changed a bit with the times.
I started doing a precision cut cutting both direction to catch any "tags" or unevenness. Looked like Mario Andretti for awhile. The when fades came in I started to cut more on the sides and let the top go a bit longer. I didn't think I could but my hair anymore after my shoulder replacement and for 4 months I let it all hang out, beard, the works. Got too hard to maintain a nice look so I barely get my arms up and around to cut the back while using 2 mirrors.
On thing about all this is that I don't like getting a haircut. I do better at the dentist. So now I've gotten a bit obsessive and do a trim at the ears (and the ear hair) at least once a week. Maybe a quarter inch here and there because your hair grows at different speeds in places and not as fast is others. I find the temples need a bit every week.
Every time I have thought I found a barber or stylist that could really do a great job the first time I wash and comb it I am back at correcting it like
@Arizona. And once in awhile I fck up and have to wait for the short spot to grow so I can match it. During COVID I had long hair and it looked like crap.
So I really upped my game and started working at it to get a look that suits an old man. I have a lot of white hair with no balding or thinning at 80. My great grandfather had the killer hair cut in the very early 1900's. The guy was handsome and always dressed to the 9's. I keep a pic of him on hand as inspiration. I don't have the facial features but I got the hair. His daughter, my paternal grandmother, had snow white hair. So that line passed directly to me AND my cousin who has perfectly straight hair. Asian straight. But he's ugly.
I could cut other's hair but I have no interest. One thing I learned is buy good scissors. $300+. You can cut a 1/16th" if you can hold it right.