my age still starts with a number less than 4.
To me, hiking means self supported long travel, possibly with an overnight and certainly with a pack that has food and supplies for a day. Daypack weight no more than 5-6kg, multi-day pack under 14kg if i can manage it (but will depend on if i've topped up on water recently)
That’s not the same as waking around a city, which usually involves much less stuff on your back, and sneakers not more technically-oriented shoes.
i’m good for about 20km/day in wilderness (class 1/2), substantially farther on class 0 (gravel paths, dirt roads,habitable places…), substantially less on class 3,4. (and i climb at about 5.9 lead/.10a follow)
https://www.sierra.com/blog/hiking/hiking-classes-defined/
I tend to prefer a bicycle to walking in towns and cities, so I don't really know how far i can walk, but it's a ways.
Like anything, routine practice and habit get you a long way. My parent is in their seventies and walks 10-15k around the neighborhood every day after breakfast. Goes through shoes pretty fast!