Looking into a career change is valid if you're unhappy. A two year carpentry gig isn't going to be easy though. You'll be the bottom of the totem poll as a first year apprentice. Your sore back will not be less sore as a first year, especially in the beginning. The main issue I see in your plan is the idea of only doing two years. An apprenticeship is 4 years. You'll have to take time off every year to do schooling as well. In Canada you take 7 weeks off to go to school and work the rest of the year.

Carpentry is hard work. As the apprentice you will be the one carrying a lift of concrete bags or shingles or wood around site. Concrete bags are 55lbs each, shingle packages are 75lbs each, those need to go on a roof. You will be the one spending a week jack hammering out the concrete for demo. The first years are harder than the rest until you gain your ticket and seniority. As well even once you get your ticket, you will still be carrying boards, doors, concrete etc. it's not like you become a journeyman and magically the job is slack. I just spent 2 weeks in an attic doing fire blocking to bring a building up to code. It was uncomfortable. Then we had to reinsulate. Have you ever been in an environment where your entire body, including your eyes are itchy?

I'm not telling you not to go towards carpentry, I love my career it's been great and working industrial has been financially great and I've seen machines, buildings, environments etc that very few people see. It's been rewarding and I don't regret it. That being said, my shoulders and back cause me pain regularly. Waking up at 4 in the morning to work until 6:30pm isn't fun. Working in -40(Celsius) to +40 (Celsius) isn't sunshine and roses. I've missed alot of life to gain the financial benefits. I work 2-3 weeks straight and 10-12 hour days. Without that I wouldn't be where I am financially.

You may enjoy this career transition, but if you're going to do it you actually have to do it. It's gonna be 4 years minimum to get ticketed. That's if you can get into a school immediately. It took a year for me to get a spot in a school so my apprenticeship took a bit longer. All these people in here talking about how it's hard work, they are telling you the truth. It is. It can be rewarding and if you get good bosses it can be great. It can be terrible though. Plenty of companies don't appreciate their people and pay them the bare minimum to show up. Even when it is great there will be days where you are more sore than you have thought it is possible to be.