Originally Posted by Schind

It's based on cycles (one cycle is a take off and landing) and flight hours rather than years and even then it's not a law.
For Airbus it's 60,000 cycles or 120,000 flight hours as long as the proper maintenance schedule is adhered to. It'll vary depending on which routes the aircraft are allocated to obviously, but at 2,000 cycles a year, which is a lot, that's 30 years. Here are some figures from 2016 of some of the oldest A320s still flying taken from MRO Management