At what age does a Staffordshire bull terrier's head get bigger?

when do staffs heads start gettin a splitt at what age about and when do they reach there full height?

They don't split. From 6 months of age, or more usually from 9 months, they start to mature sexually. One of their secondary sexual characteristics is to develop lots of muscle on their heads. No splitting of any kind is involved.

Full height is by 1 year of age. Full musculature in an unneutered male is by around 18 months of age. Please do neuter your staffies, they're my favourite breed but there are far, far too many of them being bred!!