First, 34 isn't that old. I'm in the U.S., and my experience is that a couple of years full time from ab initio (zero time) to widely employable, going at it full time. Let's say, 3 years-you'll be 37-but you'll be 37 then whether you go for it or not... What do you want to be doing at 37?
The first few years are expensive. Don't borrow money to do this, it's hard to make ends meet without pulling a tail of debt. Really important as you near retirement, also known as losing one's medical.
Really hard on family life. You're away from home a lot, or constantly moving. Most jobs are temporary, or where you don't want to live on your off duty time.