I have a relative who is a welder and I have to say, it is a tough profession that sure does take a toll on the body, as others have mentioned. Personally, I think you should look to see what else is out there in terms of trades. I know a few electricians and a few IT folks and they all seem to be doing pretty well without looking 15 years older than they actually are.
I recall when I was in high school, I didn't know what I wanted to do for a career. My Dad got me a job one summer doing manual labor. It was all I could do to get up every moment and go to work - that's how much I hated it. It was then I decided that I needed to get my shit together and get an education so I didn't have to work a job like that ever again, which is precisely what my father was hoping for.
As a father of two young sons, conversations like this do make me wonder to what degree, if at all, I should be pushing them in a certain direction in terms of education and choosing a future career. I have already set aside the cash to pay for 4 years of university for each, but I want to make sure they are truly committed to it before I sign the cheques, and if they want to do something else -- like pursue a trade -- then I would be fine with that as well. I personally loved university (all 8.5 years of it) and wouldn't trade that experience for anything, but I guess I have to realize that they may have different dreams, hopes and aspirations than I had for myself, and just hope that they make the decision that is right for them, whatever it may turn out to be. The last thing I want is two 30 year old sons living in my basement when I'm retired.