Sorry I was rushing off so it was only a quick post!
You can always have problems co-habiting geckos, they will compete for dominance over food, heating and hides. So there will always be one submissive one that won't necessarily get everything it needs. This is ultimately cause stress, and long-term stress means that they're more likely to get ill, go off food etc.
The problem that you're likely to have if they stay together is mating as well as the dominance. At a year old your male is sexually mature and will harass the female, the female at 6 months is not ready for breeding at all and this will cause complications with laying (if she produces any eggs at all).
Separating them will ensure that they won't have to compete for resources and you won't have problems with early mating - so it's better for both their sakes