With certain exceptions, the shelf life of electronic components will likely exceed your shelf life!
Over half of all the PS/2 boards I've seen that have failed had one particular cap brand that was obviously in distress, it's the WINCAP brand. Whenever I see one of those on a 5V PS/2 board, I replace it with a quality capacitor.
Well, I take some real comfort from the first point (!) and the second one is news to me but I can see what its effect is.
GRJ also mentions oxidation/deterioration of contacts and I've seen that with volume pots and sound chips on TMCC boards after no more than a couple of years' storage (in temperature but not humidity controlled conditions). Fortunately, while replacement/alternative parts have been available, I have not had anything reduced to shelf queen status.