One could argue that Justine Bateman peaked around 18. I'm not saying that to be catty, I'm saying that to set the context. If the best part of your life came before your 21st birthday, then you have mostly stuck to things that you tried, did pretty well at, and just fostered that natural 'talent' (predisposition).
If your friends are the same, then you might believe that nobody ever got good at anything by sheer force of will - which is itself a talent that some learn along the way.
It's the hare telling us that the tortoise lost the race, only because they have been napping.
There are things in my life I was instantly good at. There are ones where I had to work my ass off. I get equal praise for both and it galls me because people assume that both skillsets required the same effort. One set was a pursuit and the other was a mission. An ordeal.
Wisdom has accumulated from both, but only one of them made me a better person.
Jason didn't peak until well into his 30's. If they don't argue about this it's because Jason realizes that winning that argument will just hurt his older sister more than letting her say stupid shit (when you convince someone their whole life is a lie, it doesn't often go well).