Biker Chick Yoko looks like she has smaller boobs then teacher Yoko.

Well, yes. She did grow after the timeskip, afterall.

SBK said:
Well, yes. She did grow after the timeskip, afterall.

How? Wasn't she already like 20?

No, she was 14 pre-TS. Seriously.

14?! Yikes, she developed early.

Tetrominon said:
No, she was 14 pre-TS. Seriously.

A few fans theorize that the human's grasp of time was fucked up while they were kept underground. I go along with this, since... Yeah.

I think the whole 14 thing could still be accurate, though, from what I can remember about some girls back when I was in middle school. Sure, it may not be the norm to have a body like that at that age, but it's far from impossible.

Supahrobo said:
A few fans theorize that the human's grasp of time was fucked up while they were kept underground. I go along with this, since... Yeah.

It's not just theory, but the facts are different.
Official word is that, on the planet most of TTGL takes place in, years are longer due to the planet being farther from their sun than Earth is from its sun. Thus, 14 TTGL years = 16 Earth years.

It should also be worth pointing out that TTGL is an anime, and animes shouldn't be taken too seriously when discussing proper breast proportions.