I did it. I was past 40 when I did it, with no related experience, plus I'm 'just a girl', so, yeah, you can!
Some tips from someone who has done exactly what you're contemplating:
Don't expect to be a climber at first. Climbing is just the last part of the commute to the job site. I've met several young keeners who could get up a tree fast enough, but they didn't really have a clue what to do when they got there. You're ready to climb for money when you know how to prune properly and how to rig pieces of wood that are too large to throw. Watch people you respect to learn that.
Don't depend on YouTube. By all means look at all the videos you can, but be sure to read the comments. Treat this as background information to get a sense of things rather than a 'how to'. I tried learning footlocking from the internet and damn near killed myself or worse.
Have a 'can do' work ethic but don't let exuberance get in the way of being safe. You need to develop what I call 'field sense' in your first week. This means recognizing hazards and staying away from them until you know how to manage them... which often is still about staying away from them.
Be prepared to show up when it's hot as hell and when it's cold as, you know.
Bring your lunch.
Read things. The first three things to read are Gilman's book on pruning; the Tree Climber's companion and get a Sherrill catalog. Flip through that over and over as you get job site experience. You'll get little aha moments every time. Anyway, that's what I did starting week 1.
After a bit, get an ISA study guide. Learn everything in that. All of this is just a starting point.
Go to a competition just to observe.
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