CUDA generally doesn't enforce any maximum driver version.
Older CUDA toolkits are usable with newer drivers.
The only thing somewhat relevant here is that eventually, from time to time, NVIDIA GPU architectures become "deprecated", and this usually happens first at the driver level. That is, a particular GPU may only be supported up to a certain driver level, at which point support ceases. These GPUs are then in a "legacy" status.
So if your GPU is old enough, it will not be supported by newer/latest drivers. But if you currently have CUDA 7 running correctly, you would have to at least have a Fermi GPU, which is still supported by newest/latest drivers. However Fermi is probably/likely the next GPU family to go into a legacy status, at some point in the future.
