I don't think you should rush into anything  I don't Probe my GTP's  till they are  much bigger  ,,  probing a small  Chondro  can cause  damage   better safe then sorry  ..  i would wait till it's at least 200 grams    but I always opt on the safe side  .. you should start seeing  signs in the sheds soon  ..

I actually have the same issue. I have the tools, know the methods, but never actually did it so I lack the confidence. I know what I been told when I bought my snakes & seen what leads me to believe it's true but it's hard to take anyone's word especially when it's easy to make a mistake. I know a few folks from here & similair sites attend local reptile shows. When the time comes I have a few plans.  I'm hoping, I'll have a few more friends locally that are willing to share there experience by then but if not I'm sure there will be a reputable breeder at a local show that will land a hand.

+100 to chris and mike!

While some keeprs push things a bit you probably don't want to breed your males until at least 3 yrs old and your females until at least 4 (taking weight into account also).  So by the time your snake is 3 yrs old if you still haven't seen sperm plugs then you probably have a female.

Yeah, what everyone else said here. However, it's nice to know as soon as you can so you know what to name them. I know my girl Oscar isn't really happy about that.

Also, lemonhead is a boy.

before I award these points, Aaron why do you believe its a boy or is this just a guess 

Im also looking to pick up some babies this season (just throwing that out there) if anyone has anything in the works 

Because he looks like a boy. You feed well and he's got a boy's body shape.

50% of the time, i'm right about this every time.