I've had a planters wart on my foot for 20 years. is this dangerous?

Planters wart: No. But they usually are gone after about five years so perhaps get examined to be sure what it is

Location, Location.: A plantar wart is actually a virus infection. I have never known one to last for 20 years, at least stay in one spot and not spread. More than likely, a more likely scenario is a intractable plantar keratosis ( IPK ). An IPK is generally found beneath a weight bearing bone. It could also be a foreign body. To remove all doubt, have your foot evaluated by a foot specialist.

No: If it were, it should have caused damage long time ago, see a podiatrist or a dermatologist for managent, best wishes

No: If painful or bleeding it could be treated by your PCP or a podiatrist