For both the earliest I have heard of males going is around 18 months, and they are usually pretty easy to get to go at this age as long as they have had decent feeding throughout their lives. Females on the other hand are difficult to get to breed at 18 months. Does happen every once in a while, but not often. Most will be ready to go at 2.5 yrs with decent feeding.

As for weights, here are weights I would shoot for, although I do know some have gone at lower weights, but these are what I would hope for:

Coastals, males 800g, females 2000g
Irians, males 700g, females 1500g

I think I remember reading about an IJ male going at less than 500g, but that is a rarity. All the coastal males i have bred have been well over 1000g, so I don't really know a low end on them. And you can try females at weights lower than these...but in my experience they usually don't do anything or slug out.

GOOD LUCK!