In my late thirties. I didn't stop caring, I just got so full caring about other stuff—wife, kids, family, career, various projects, etc.—that I just didn't have as much capacity left to worry about what people think about me as much.

Give it another year or two. Turning 30 in a few weeks, can feel the caring beginning to evaporate on its own.

When you stop trying, you'll know you've stopped caring.

I'm 26 and I almost nearly don't care and can't relate to half the things the article said. According to (unscientific) Myer's Briggs, I am very strongly introverted, however.