If it been in an airtight jar and not got damp or bug infested then oat will keep for many years and be quite safe to eat, it will lose a little flavour after about 10 years but extra sugar should fix that, so don't worry go for it.
There are two tests for iffy oatmeal:
test 1. Sniff it. Sniff hard. If there is no hint of fustiness, proceed to test 2.
test 2. spread some of the oatmeal on a flattish tray or big plate, making sure you use some from the very bottom of the jar. Look very carefully, with magnifying glass if necessary. If anything moves, it has weevils and the birds will love them. If nothing moves, the oatmeal is fine.
And bayleaves will keep weevils at bay, keep them in your panty (open to the air) also in wrap in cheese cloth and stick them to the inside of you jar lids that you keep you flour and pulse ect in. change them every six month or so and you willbe weevil free