If the wood is stabilised, i.e. resin-impregnated, then it should never need any treatment, other than perhaps polishing if it gets scratched or dull.
If it's finished in some way, you need to know what the existing finish is. If lacquered or varnished, oil won't penetrate, so won't do any good unless you remove the surface finish first. If it's bare wood or oiled, you can apply more oil. I'd avoid a vegetable oil like olive oil, they can "go off" over time. If you want to use a non-setting oil, you can buy something like salad bowl oil, or mineral oil (sold in pharmacies as a laxative). I believe some nut oils are also resistant to going rancid. Personally I like an oil that cures to a harder finish like Danish oil or Tung oil. But as mentioned previously they will usually affect the colour of the wood to some extent.