I left an office job in my late twenties for a career change into arboriculture. A good place to start is the Arboricuiltural Association.
You’ll need to get trained on chainsaws, wood cutting, felling, and climbing with a saw. Probably best you get aerial rescue too.
It is very physically demanding and you’ll take perhaps 5 years to be well skilled and experienced. I lost two stone in the first year. But then I probably needed too!
Good luck – I haven’t looked back but I’m now in my forties and don’t work on the tools anymore. Still working in the industry though.
Happy to answer any specifics if you want to email (in profile).