geoff at 28 years old im kinda in the same boat. i went to school and graduated as an automotive technician, i then decided to tackle a different trade and opened a contracting company. a few years ago i had my life sidelined by a drunk driver who put me in the hospital and turned my life upside down by breaking my neck.
im now recovering, i am able to look for work but cannot go back to my trades as my back wont handle it. thus far i have not found anything. im gonna end up going back to school at trying my hands at some type of office enviroment/sales training.
as humans we are very resourceful. when one door closes another opens. you say you like building things? well why not give carpentry a try? there are unions out there that do some major training and job placements. or how about finding something you are great at building and getting a market for it? a friend of mine is incredible at building desks, and chairs. he's now got a business that sells to a higher end market doing great for himself.
im sure in the end your determination and smarts alone will net you something that you will enjoy.
cheers.