Ours will probably happen before the Flex implant reaches it’s middle age crisis! 
Jokes aside, these implants hardware have no “mechanical expiry date”.
The ones you see with an expiry are usually payment implants, and that’s entirely due to an arbitrary limit imposed by the likes of Visa on how the tokens must be issued and embedded in the chips.
Or maybe implants dependent on certain software ecosystems.
This thread might help put you at ease as well:
It’s not about the flex series, but it does showcase how much effort DT puts into making sure these implants can last!
Also… Welcome!