Husband had it done when he was 19, a joint decision by both of us before we were married or sexually active. Neither of us wants kids, I have rheumatoid arthritis, and we have concrete plans to foster/adopt teenagers later in life. It's been 7 years so far and we haven't wavered one iota on what we want in life.
People have been telling me since I was 12 and first said I didn't want kids that "you'll change your mind when you're older." 14 years and I have not once had a moment where I though, "maybe, just maybe, I want to bear my own kids." Some of us just are wired differently, and there is nothing wrong with that. You do have to accept that most people are so biologically driven to have their own children that they won't understand where you're coming from and will tend to argue with you or look down on you.
For that reason, if people ask you casually whether/when you're going to have children, just say, "we're unable to have children but we're thinking of adopting." You are technically unable and people don't tend to press on what they think is a sensitive subject.
[edit] Oh, and the doctor didn't give us crap at all. Asked a few questions to make sure we totally understood the ramifications (low success rates of reversal, etc.), double checked that we actually knew what we wanted, talked to my husband alone for a few minutes to get an idea whether he was being pressured into it, and then did the operation. Total cost was something like $1,000 out of pocket (he wasn't yet on my insurance.)