"Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something."

https://news.ycombinator.com/newsguidelines.html

This isn't (or shouldn't) be an age thing. It is a 'stage of learning" thing.

If you are new to Linux (or even all Unices) and you want to get a firm understanding of the fundamentals, it may very well be worth while to go through it at least once and see all the moving parts. And see them in an order that makes their dependencies clear(er).

Once you know all that and just want to keep up with the constant churn of versions to keep that one webserver running and recent? Yeah. Not worth it. Get some distro that matches your preferred characteristics and stop worrying if you need to update libBLA to recompile Apache to fix the path traversal vulnerability. That also removes the question if that library still compiles correctly with gcc 7 or if you need to upgrade to at least gcc 9...

Edit: Doing it in a VM first, might help in getting the 99 percent working first linux installation into a usable shape to make it a good daily driver. In that sense it helps lowering the barrier to actually switching later on.

Yes, adults should not experiment with building custom distros... as we all know all existing Linux distributions were built by teenagers.

My company is looking for someone to build a linux system for a specialized tablet PC, with, among other things, a custom kernel and OTA updates.

If you built a linux system from scratch, this will put you in a very good position to get the job.

Adult people do stuff for fun, I guess.