I th8nk it greatly depends on your height. Also your gender and body type.

As above it depends on your height and body type

I think it's more, how much excess fat is unhealthy. Bodybuilders and sumo wrestlers are usually quite heavy, but are relatively heavy. And a certain level of fat is required to be healthy

If your too fat that it makes it hard to do exercise, that's probably too much

Your BMI over 25.

that's not entirely true. That's only for adults, before then it changes each year

I don’t think bmi is a true indicator, someone could be naturally chunky but not really over weight