A dialogue to avoid

My colleague bursts into the room with the news that another colleague will have her 21st birthday soon. "She's so young!"
I lean back in my chair and think of when I was that age. "Incredible, isn't it, that we used to feel stressed already back then."
That didn't sound quite right. My colleague doesn't respond. Savouring a sip of earl grey, I have another go at forming an appropriate response.
"Back when I was 21, I still believed I would start my own business as a philosopher."
"And look at you know!"
"I would've been so sad to see I had turned out as a marketeer, all corporate and what not! I would've wondered where it had all gone wrong."
We laugh a little as we turn to our screens. But why is that funny? Shouldn't it sadden me? With a big gulp, I finish my tea. No, I don't have to be embarrassed about the choices I made. I would love to have a full-blown argument with my former self. And knowing her, she probably would too.
But I can't quite shake the sneaking suspicion that, if I let her, she would change my mind. Because really, what insights and learnings have I reached in nine years, that could possibly change her mind?