A well-maintained TPE doll can last anywhere from 2 to 5 yrs. Silicone dolls can practically last indefinitely, but on average 10 yrs is absolutely normal.
This all depends on how rough or gentle one is with their dolls and how much maintenance, care and upkeep they provide.
Fun Fact: There is a silicone doll that is currently 12 years old and still going strong.