I agree, she looks at least 6 months. Very healthy looking and appears to be sexually mature
First if you're breeding you'll need to make sure she's in the mood. If you put her together with a male and she acts aggressively/stressed (dark colours, hissing etc) this is an indication she's not ready. Their colours generally change when they're feeling broody as well as when pregnant (normally bluish tinges), and she should remain reasonably placid with the male (granted she'll make him work for it! haha)
When she needs to lay her eggs (fertile or not) you may notice her scratching to get out the cage and/or scuffling around the bottom of her cage. Make sure you have her damp sand box set-up so she can peacefully lay her eggs with no stress. This is very important, as females are known for retaining their eggs if they're not happy with the husbandry, which inevitably can kill them.
Here are two great posts by another member on how to set-up her sandbox, hope it helps!