question between novice and amatuer

[Spiderman]

GTU basically means 600cc inline-four's & under
GTO means unlimited cc's

Novice GTU/GTO can only be raced by novice racers
Amateur GTU/GTO is a mix of novice and expert racers.

Yes, a first-time (novice) racer may race in amateur.

That's pretty much it, with certain exceptions depending on your bike (not sure cuz I don't have any first-hand experience in this area, but I think Modern-Vintage might be a valid example). In cases like that, I think you may also need special permission from the New Rider Director, Mark Schellinger.

[Spiderman]

and what else can a first time racer race in?

That's pretty much it...

Oops, I forgot - a novice is also eligible for Sportsman and Endurance classes.