After a second of thinking, I answered "Having fun."
I asked him the same question back and he said "Having an impact on the world."
Although I don't think about it that much, I realized that I personally didn't care that much about my impact on the world. Any impact that I create would simply be a byproduct of me pursuing whatever activities I find fun.
Moreover, a positive impact in my eyes might end up being a negative impact to others. The road to hell is paved with good intentions.