But if a 20 minute old clone is perceivable as a 20 year old human, doesn't that mean that a 20 minute clone can be perceived as a 20 year old human, and so the perceived age of the clone by an observer is 20 years?
One can claim that real age is absolute while perceived age is relative. Let's take for instance the movie Blade Runner.
***SPOILER ALERT*** Do not read below this line if you haven't seen this movie and don't want to know the plot.
In this movie, artificial humans are manufactured as a cheap and efficient labor source. The differences between them are mental only- an artificial human has no life experience and so fails certain forms of mental tests such as for emotion. An observer looking upon an artificial human would be unable to tell a 3 year old one from a 25 year old human, therefore they observe, they perceive the age as 25 years old. This is further complicated by the revelation that a new class of artificial human had been created that has memories. The one introduced is so real that it passed the emotion test, and our protagonist didn't even know she was manufactured until he was given that information. Her perceived age was so realistic that *she* thought she was really over 20 years old, instead of just a few years at most.
Given this, even though perceived age is not real, and is relative to the observer, it has real consequences. Another example is the antiquing process of making replicas look old. It's not real age, it's only perceived age, but it can have real monetary consequences.