old Mac

We have a '91 Mac that we keep all farm records on: field, maintenance, livestock, feed, landlords, income, expenses, etc. It does what we want. We've had no problems. My husband is comfortable with it. However, our college-age son says that at that age it is a time bomb waiting to go off. We have a newer PC, an off-brand, which our son wants us to copy all our records onto, and use. My husband considers the Mac as reliable as the PC, or even more so. Any thoughts? How long is an old Mac useable? Any warning signs?

Thanks for any help.