[Nebulas]

You can either move a normal move (up to 12") or you can choose to turbo-boost - in which case "A unit using turbo-boosters must end its move at least 18" away from its starting position...".

That sentence finishes: "...to claim this Invulnerable Save, as it relies of flat-out speed."

That makes it seem to me that that sentence is criteria for claiming the Invulnerable Save, not a statement which is intended to limit the minimum distance covered in a turbo-boost.

 

[Caluin]

It's also worth pointing out that (jet)bikes cannot move any distance between 12" and 17.99".

You can either move a normal move (up to 12") or you can choose to turbo-boost - in which case "A unit using turbo-boosters must end its move at least 18" away from its starting position...".

When you quote a rule like that, you must take into account everything leading up to that rule, and everything preceding after that rule. You can't just take a sentence out of context of the entire paragraph. It tends to change meanings when you do that. This is exactly how quotes by Movie Stars and the like get mis-quoted.

Two things - first, as Nebulas said, you conveniently left off the part that says "to claim this Invulnerable Save." This sentence obviously is referring to the criteria for treating your armour save as invulnerable.

Secondly, and more importantly, a couple of sentences earlier in that same paragraph -
"When using their turbo-booster they may move up to 24" in the Movement phase." The important words in that sentence are bolded.

It was a nice try, but no dice.