Did you mean to ask "how old are you that you can't do [something you've never done before in your life and thus don't have the muscles for it] for five minutes what an 80 year old [who has done it every day of their life and thus has the required muscles] can do several times a day"?

Also, I'd like to point out the differences in length of time between taking a shit and a normal 8 hour work day.

I'm not saying this is impossible, but I understand the trepidation.

Same goes for sitting toilets though.

And we still don't have any arguments supporting either position. I do squat for a few minutes every day to facilitate my squat lifting workout but don't see an inherent benefit. I suppose one can argue that it has been a natural movement for so long that our bodies may be genetically designed for it.

Look at young children, and see how effortlessly they can sit for ages in squat positions while playing. After I started fixing my squat for lifting, I've noticed I now often naturally squat down instead of awkwardly contorting myself when playing with my son for example.

My mobility is still poor compared to what it was when I was a child, but at 38 I'm now finally more flexible again than I was at 25, maybe more so than at 20, and it's great to not feel constrained by weird movement patterns.

they have very short limbs making this very easy

Their limbs are proportionally the same, and their muscles equivalently smaller and weaker. It's no harder for an adult with proper mobility.

it completely depends on the proportions

long-limbed people have more difficulty with this, while shorter-limbed people don't have difficulty with this after a little stretching

Same in Japan. It's also pretty common to see people squatting near buildings for smoke breaks, etc.