I always lived below my means, but only made it a priority in the last few years. Was in school until 25 (Master's degree), and maxed out my IRA during my late 20s. Enough 401k contribution to get the match, but nothing Mustachian. So I had good habits, but not great ones.
When I was 29 I spent a year working in Italy, which included a 1 year $50k reduction in salary. I did it because I always had the philosophy that life should be about life, not about money*. And spending a year living in Italy was cool. I'd do it again.
Since getting back from Italy, early 30s, I've made living below my means a priority. Suddenly I'm investing >50% of my take home, and am on track for FI around 40. This is while living in a HCOL (Northern CA) area. If I decide to move back to MN (Grew up near the Twin Cities), with it's lower cost of living, I could hit FI a few years earlier.
Even though I'm now much more aggressive about saving, I still wouldn't say that FIRE is a huge goal for me. FI is, though. This is ultimately because I like working. I'm in engineering research, and I get to do some cool stuff with some cool people. I like being creative and innovative. I like teaching people the things that I know. I like helping solve problems for my colleagues. What I dislike is the corporate environment, and all of the completely nonsensical expectations that come along with it. So my goal is to have enough of a stache for an absolute bare bones FI lifestyle, which gives me much more control over my work life. Then I can go independent, and do the projects I want with the people I like. And nothing else. I'd get less work, and have less income, and that would be just fine because my stache would be enough to live on.
*Yes, clearly these two impact each other. A lot. I guess what I'm trying to say is that, while I'm certainly not willing to go into debt or be a spendypants, I'm also very willing to be a less aggressive mustachian in exchange for really cool life experiences.