How long do you expect a mattress to last

I got mine from my parents, when they got a new mattress about 10 years ago they gave me their old one. I assume mine is at least 15 years old, almost 20. I can probably get several more years out of it as it has no problems. Is this a normal lifespan for a mattress (20+ years) or did I get lucky?

I’d say a matress is ‘good’ for about a year and then ‘useable’ for 10. Depending of course on the quality of the matress and the weight and sleeping habits of the user.