in fact he begins to get younger at certain speeds
The rest is true that statement part isn't .. you can only get the aging to zero .. you can't get younger that only happens in the movies
My answer only refers to proper time, I have no idea what that means with "Bill S time" and "biological time" or "Paul time" as the definitions aren't clear to me.
If you want to do a Bill S tachyon and get the younger state. You theorize you can go faster than light speed and use some extensions which have no experimental evidence, and thus create something which is called tachyon. So you suddenly go from being made of matter, get converted into tachyons at a particular speed and then start going backwards in time. It's a nice movie story but I think my invisible pink aliens or your GOD is better story than that, I might want some evidence.
If you want a scientific criticism of tachyons then it is that is is an extension of GR and as such the
theorized particles are not quantized. So although you can conceptually do such a thing in GR there is currently no known way to do it in QM. Even string theory which has not been able to successfully incorporate tachyons although there are ongoing attempts because some want to believe it could be true. The common approach is to have a tachyonic field (which is easy) but having a tachyonic particle in that field generally leads to instabilities. So those proposing the idea need to show us how it's possible to get stability and give us evidence we could test for.
For Bill S: The Higgs field in your classical world must be tachyonic, you might want to read up on why. Be careful not to turn this into a kinematic motion, the naive idea of a field moving like light across the universe is grossly wrong. Perhaps turn it into a field vibration on the stationary spot which would work better but still isn't accurate as the description really isn't about motion but about stability and time when trying to drag this back to classical descriptions like GR.
Finally for Paul, I don't have the ability to ignore experiments like you do, so contrary to your claim, I expect absolutely nothing of you
