The person who knows cursive can go on to learn Newtonian physics. Now he knows two things. While your supposed hero still only knows one.

Once upon a time, I thought I wanted to learn cursive handwriting. Except this version of me was already in his 20s, would be out of school in a matter of months, and quickly realized the skill would be of such marginal utility in the future that it wasn't worth the hours spent tracing out giant letters like a kindergartener every day.

One could learn this skill in their 20s or beyond, but there's an opportunity cost – why not something else that would actually improve work performance, or that you enjoy doing?

I still wish I'd been taught in elementary school, though, because it would've been really useful as a student. Some of our teachers discreetly handed out practice booklets to students who'd "expressed interest" (their parents taught them the basics and teacher noticed); most of us were not so lucky.

The person who knows physics can go on to learn cursive, should they choose. "Knowing cursive" is not specially indicative of one's intelligence.