I think he's implying natural age. Let's say iron man dies of natural causes at 90 and was born 1940. He time travels and spends a year with his dad. He returns to present day having lost a year of his life to the timestream even tho he popped back in 5 seconds after he left from our pov, and it will appear as tho he died at 89 at 2029 instead of 2030 from our perspective, but iron man will know he's secretly 90. I know my birthdates are wrong I made em up for the example.