I live in a city with mediocre to poor bike infrastructure at best, and I see plenty of 50-70 year old women doing 25km/h on ebikes or 10-15km/h on regular bikes.
Granted I wasn't overweight when I started, but after 5 years of largely being a couch potato and doing office work, I averaged around 20km/h or ~12mph door to door over a commute of 10 miles on a 40lb trike.
After getting fitter I'm about the same speed but a shower and change of clothes at the other end is optional now even on a 32C day rather than being drenched.
Your experience can only be due to bike hostile infrastructure or laws. If you had to stop three times for 2-5 minutes a piece at each intersection in a car while the empty lane for bikes and pedestrians got a green light on the off chance they showed up, you'd probably be complaining about how inconvenient driving was.
General population would struggle. I used to bike commute twice that distance regularly and think that'd take me more like 25, maybe 30 now that I haven't done it for almost 2 years.