The quality of the mattress can be a deciding factor on how long your mattress lasts.
Lower end mattresses may only last 5 years before wearing out while higher end mattresses should last between 10 to 15 years.
Either way it's not a good idea to keep any mattress longer than 15 years since by the time 15 years have passed the mattress will be disgusting anyway because of bodily fluids that can't be seen but was absorbed by the mattress over the years.
After 10 years though I'm always ready to purchase a new mattress along with a new bedroom set.
10 years is a pretty long time after all especially for a mattress.
Replace your mattress every 10 to 15 years and you'll likely even sleep better.