Whenever you like. I'm not sure if you others meant this but I'll explain.

A sailor's ability is recalculated every time he levels and at the moment you put the
boost on. Weather you boost him at 120 or level 1 it will make absolutely no difference
by the time the level 1 hits 120.

I hope that's clearer.

as soon as you can =)

Level 1 is the best level to boost them...

I asked this question not long ago. .

You can boost at any level.. It won't matter. It won't affect the sailor stats if you do
it later or early.

Doing it early just allows you to have better stats now instead of later.. It increase 20%
of your stats.

I would boost the fighters, as its a eating frenzy out there with fter stats, and as from
my research from other posts, it seems that bomber stats are not really a big deal.

correct my if i'm wrong.