I guess has Khan had '5 times the strength' of humans it's reasonable to assume he's x5 with everything else too, so a fifth of the time? Whatever that is...
And which his magic blood, did Khan even have a "life span." Immortality.
From the start of the industrial revolution until the landing on the moon it was two centuries, Khan and his people (and their growing population of children) might reach that level of technology in a single century. From the moon landing until Cochrane's warp flight it was one century, Khan might cut that by two-thirds.
By "post-Nemesis" Khan is free and could have a fleet of starships.
And of course his savagery.
... the future Starfleet/UFP does not execute prisoners ...
What could possibly make you think so?
This is entirely separate alternate universe, a decade before the prime
universe only had one death penalty offense on the books. Once the list of his offense was read (in a secret Starfleet court) they'd be executing Khan by phaser right there in the court room.