The thing about prostate cancer is that it typically has no symptoms at all. Your brother may well have prostate cancer - most men his age do have it - but it's almost certainly not the cause of the peeing problems, and if he does have it, it doesn't necessarily mean that it needs any treatment. At present it sounds as if the GP is trying to find the reason for the peeing problem rather than rushing into cancer diagnosis which may be unnecessary.
Prostate cancer occurrence goes pretty much in line with age, so around 60% of men have it at age 60, 70% at age 70, and so on. Most will never know that they have it, and it won't kill them. It's a very slow-growing thing and a delay of a few weeks will do no harm.
Best wishes,
Chris