Fridge problem. I have a hotpoint side by side model #CSX22BCXA bought around 1995. It has worked

Question

I have a hotpoint side by side model #CSX22BCXA bought around 1995. It has worked great but now the fridge is starting to lose its cool and the freezer isn't staying cold enough to keep stuff frozen. There is frost building up on the back wall of freezer from top to bottom. Everything seems to be running. The outside walls of fridge are still chilled. Can you tell me what's going on?Thanks,Paul