I don't know exactly when I built my first smoker - but if I had to guess I was about 12. My father was a rancher (which meant he had a day job too). We needed to maintain some stuff, so I bought a welder and found a class at our local HS for adults (and brought me to class with him). We got some practice bits so I could work on my beads at home, and a week latter I was repairing farm stuff. By the end of the month I asked him if I could build him a BBQ pit. We went to the metal yard and had them do the cutting, all I did was simple assembly.
I am about 45, and the pit is still in the back yard. I don't use it much though, it is NOT set and forget. I am tempted, however to re-weld the fire box - as the rest of it is still tight, and I could easily put a stoker on it and keep on smoking. It would only be out of nastalga though - I have a UDS, will finish a MUDS this weekend, and hope to get a BGE shortly.
If you live in a city, look to see if your community college offers classes. There is a good chance that if they do, they might also offer practice facilities. Informal classes might be ok to get an idea how to start, but if you look, you can probably find either vocational or art classes that go far past that.