It's surprisingly easy to learn. I had a coworker who did this as a hobby while working in tech. Rolex hires people right off the street and trains them into professionals within weeks. Even as an amateur I've opened a few of the cheaper watches in my collection for some basic maintenance. When I retire it's one of the hobbies I hope to dive deeper into, it would be nice to be able to do my own oiling on most of my collection.

The main barrier to entry is that you need a lot of tools and supplies, I priced it out and to do a full service on an automatic I probably need $1000+ of tools and supplies.