Hi Kieron, sorry to read about your Dad.
39 is indeed young for prostate cancer , I was diagnosed with aggressive prostate cancer age 49 that was 2 years ago, I have since met men aged 43 with aggressive cance too however it is not very common in ones 40s.
The PSA test is indeed only a sign post and please remember this forum does not have medics on it just people who have or have seen the cancer so take all advice in and make your own decision.
Statistically, roughly 1 in 8 white men get prostate cancer , 1 in 4 black. If your father has it that risk more than doubles (my father had prostate cancer too) so personally I would discuss with GP too but I think I would be going for a test regularly in my 40s because if you catch it early it is curable,(my fathers was) or too late and it is not (like mine and sadly your Dads) . By the time I had symptoms it was already too late, if I had been told about the risks I would have been having tests earlier and who knows.
The downside about a PSA test is not the test itself but afterwards if you have a raised level there are mental challenges and a biopsy at some stage that has risks attached but ignoring it may just be building a time bomb .
I am sorry that this is not the happiest post you will read but the facts that bother me for my kids are early diagnosis should cure a man.
Speak to your GP
Sending you and your father every good wish
Kev