Welcome to the forum. I would say go to college and get at least an AA degree. While at college you can check out scuba diving to see if you like the water. The reason for this is that there is a good chance that when you start a diving career that you won't be doing it in a year. I've been in the Gulf of Mexico for the last 11 years, I started a couple of weeks before I turned 27. In that time I've seen many more people quit within a year than stayed. Before I start answering you questions, you'll be a construction diver that specializes in underwater welding. There on only a few dive companies in the Gulf of Mexico that offer underwater welding, if you go inland there are vastly more companies that offer the welding. Which is better inland or offshore? That would depend on who you talk to, if you started your career offshore you would say that was better, if you started inland you would say that that was better. From what I've seen and talked to, doesn't matter. At least offshore you can see most of the time. In last, if you decide on diving, keep you ears open, ask questions, the only stupid question is the one that you don't ask, and learn as much as you can.
1 - Depends on how many days offshore you want to spend and the amount of jobs that year, like every thing else the oil field has its ups and downs, but realistically from 50k to 200k. The first couple of years will be on the low end. You'll have a diving rate and a welding rate, as far as the amount of difference, that would depend on your welder status and tender or diver status.
2 - If you don't go offshore you don't get paid, so if you've got the money in the bank you can take off as much time as you want.
3 - Math would be good, but not necessary, just a general education is all you're going to need. College is if you don't like the offshore thing then you have something to fall back on. Like I said I was 27 when I started, I've got a AA, AS, and BS. If I don't want to do the offshore thing I can do something else without someone telling me, if you only had some college.
4 - You would have to first go to dive school, there's a few of them here in the states, east west and south. All of the schools touch on wet welding, but what they got over you might as well not pay too much attention. You will have to go thru the company welding course and learn their procedures, and it's not even close to what the dive school tells you.
5 - In my experience in teaching the welding school at the company that I'm at is the fella with that least amount of welding experience picks up the wet portion faster. But one of my good friends has a degree in welding and he picked it up in a week, go figure.
6 - Age range in dive school is 18 to 40. I start dive school when I was 25, the next oldest was 20 with everyone else 18 to 19. My class started out with 43 people first day, on graduation day there was 11 of us left. Out of the 11, 7 came to the Gulf of Mexico. After the 1st year there was 3 of us left, after 5 years only 2 of us.
Hope this gives you some answers that you're looking for. I'm sure that you'll have some more questions. My email is, c_welch@bellsouth.net . If I don't answer right off it's because the internet out here is on the fritz, at least now offshore we get internet.
Charles Welch