Time Paradox

This is kind of a tough one to explain, but it's a paradox I came up with while watching something that had characters in a different timeline.

Here's an example of this time paradox:

Billy is 17 years old. The year is 2022.
I am 15 years old. The year is 2015.

By the time I reach the year 2022, I will be 22.
However what age will Billy be?

Will he be younger than me at that current time or continue being older than me because he'll continue on in his own timeline?

That's right, I just blew your minds. Do you think you can solve the paradox?

 

So parallel universes?

 

Billy would be 24 years old, regardless of the timeline he's in.
If he were somehow transferred to our timeline, the years he has already lived wouldn't just go away, and therefore he would still have 17 years of age.
By the time you reached 22 years of age, if we assume Billy had transferred here, he would be 24 because 7 years would pass for him as well.
And if he stayed in his timeline, he would still be 24 because those 7 years would have passed there as well.

If you got 2 timelines, time flows the same in both of them. It wouldn't just stop for Billy if you continued to age here.