No, there is no way to know the age of an iPhone. The IMEI number does not in any way tell you this. Its just an ID number for the cellular carriers.
You can enter your serial number here:
Check Your Service and Support Coverage - Apple Support
and if it says its still under warranty, you can assume its less than a year old. or less than 2 if it has Apple Care+.
Beyond that, there' no way to specifically know the age of the iPhone.
Why do you need to know it?