Most people, especially past a certain age, don’t run distances. A mile is a long distance to run for the average person (across all ages). We don’t need to gatekeep physical activity.
But fortunately you don’t need to be a runner to be active. Walking is substantially better than sitting.
If walking is considered being active, we have vastly lowered the bar.
I know literal 70 year old people who could out-run 20 year old kids because they made the choice to stay active and healthy in old age
Even a casual stroll will raise it noticeable, and my normal medium-fast pace can easily bring it to 100+ bpm. (My resting heart rate is generally around 55-60 bpm.)
As for my estimate of my fitness, I think just the fact that my resting heart rate is below 60 might suggest something to that end.
Nope.
https://www.cdc.gov/nchs/data/nhsr/nhsr041.pdf
Even for someone who's 60+ and in poor shape it's unlikely to be that high, so getting it up to 100 would be an improvement and have positive health effects. 100bpm doesn't even count as zone 1 for me, but even so a half hour or more of walking at a pace sufficient to sustain that is clearly better than remaining stationary.
Every physiologist who has ever taken quantitative measurements of these things would disagree. Walking is definitely better than remaining stationary, with significant measured benefits from even modest time per day, and GP is right that those of us who can do more should resist the temptation to gatekeep (usually done in this case as a low-key kind of bragging).