No the issue really becomes slots and power.
If you have only PCI slots (not PCI express PCIe) then that can be a problem.
If you don't have enough PCIex16 slots you will need extenders and a little jurying rigging.
If you have 2+ PCIex16 slots the age of MB is irrelivent.
Mining uses so little bandwidth you could run 20+ GPU on a serial port if such an adapter existed.
An older computer may not have a power supply capable of pushing multiple high end cards so you could be looking at a PSU upgrade.
Take a look at your PSU. Find total wattage, find how much wattage is available on 12V rails. Find out how many 12V rails there are. Take a look at the MB. Do you have any PCIe slots? How many? In which slots? What length are they? PCIex16? PCIex1? Post that and people can give you some idea of what your options are.
It could be anything from "drop in ready" (buy 1+ cards, plug them in and mine) to "it would be cheaper to start with a new rig".