I've been playing a Half-Life mod called Sven Coop since 1999. I play almost daily, if only for a half an hour when I get home to unwind. Multiple server owners have given me admin rights to help manage their servers so sometimes I'm just there to kick griefers or change levels that are broken so people don't leave. There are many thousands of user made levels. People are still making them. The mod is still getting updated. Just did actually.
It wasn't added to Steam until 2016. So there was no way for me to track play hours until then. Since 2016 it shows that I have a little over 3000 hours. And I used to play more before I became an adult and had to do adult things. So I can only imagine what my total hours are.
10,000 hours? And that's probably conservative.
I will have been playing regularly for 26 years this January.