Almost every 80 year old man has prostate cancer - it's essentially a matter of being a man and living long enough, so in that sense it's unsurprising that a potential tumour showed up on the MRI. That doesn't mean that any treatment is required, though; the majority of men with prostate cancer never know that they have it and will die with it not from it.
If cancer has spread to the bones, one would expect a PSA in the hundreds or even thousands, so I wouldn't be too concerned about that. If the biopsy does show cancer (and at his age it probably will) they're likely to do a bone scan, but it's a purely routine part of the diagnostic process, so don't worry about it.
Best wishes,
Chris