Focus Distance

Ever since I was little, I liked to see what I could do with my eyes. Cross them (which I learned from Mom), shake them (which I learned from a fellow fourth-grader), focus and de-focus them (which I think I’ve been doing since I was three or so).
I am 36 and have managed to avoid needing glasses so far, but I wonder how much longer I can go. I think my Mom made it to about 40, and I’ve heard that your lenses harden gradually, with 40 marking about the limit at which you can focus both close-up and far away under your own power. The question I have is this: can you postpone reading glasses by exercising your lenses? Does flexing them deliberately have any effect on their pliability? I have been habitually de-focusing (blurring) my eyes every few minutes or seconds, for years, perhaps with that hope in the back of my mind. Does anybody else do that?
Here’s a test: what are the limits of my focusing? I can see far away clearly, but how close can I go? I remember it was as little as two or three inches once upon a time, but I’m sure it’s much less now.

Seven inches. Same in both my right and left eyes. Maybe 6 3/4 on the right. Any closer and I lose sharpness. I’m surprised—I didn’t think I could still focus that close.
I should keep track of it—it might make a cool graph.
I heard that one of my male ancestors (maybe my Dad’s Dad’s Dad?) kept holding books farther and farther from his face when he read, until he got to arm’s length and couldn’t hold them any farther. At which point he relented and got reading glasses.
Do other people do that de-focusing thing? I asked Georgia and Maya; Georgia (age 8) didn’t know what I meant—the only thing she thought of was squinting. But Maya (age 5) did, and demonstrated by getting a vacant look on her face for a moment. I encouraged her to keep up the skill (de-focusing; not looking vacant).