I thought I might reply since no one else has, although I am definitely no expert - I have been told that they should be about a year old and above 50 gms, they will mate before this though but isn't a good idea as will not do the female any favours. Hope this helps
Yes, 50 grams is the most important factor, as breeding smaller geckos can cause a laundry list of problems, even death. Also remember not to house a male with a female until you are ready to breed, because even if they are too young to breed, the male will try to anyways (males develop sexually at a very young age).
Jess - just posted a thread with regards to my 2 geckos about their behaviour - do you mind having a quick nose at it as you obviously know what you're talking about