HOWEVER, here's another solution:
Bert could be on planet Venus, and you never said 20 or 23
years old, so we could be talking about days. So 2 days ago he was 20, now he's 22. If he were born towards the beginning of the year, next year he'd be 23, because a day on Venus is longer than a year.
OR (a much simpler explanation):
You're talking about days, his birthday is December 9th, and it's the 31st of December. (The same thing could be done with months, or any other unit of time.)
And yet still:
The guy's current name is Bert, but two days ago his name was 20. He's decided that next year he'll change his name to 23.
Oh, and I see why someone might be mad at B Boy himself posting the answer (which he edited out

), but what's wrong with Vraslosken posting the answer? If you don't want to know the answer, don't continue reading the thread, silly.