Hi,
is the mileage in you sig correct ? 450,000 km ? (=280k miles)
if it is, then I'd say this is not an issue. I'd say with larger miles on an engine then the oil light being on during tick over is not a problem. If it comes on at any point with the engine running at over say 1500 rpm then I'd start to worry.
If you want you could get a pressure gauge fitted to supplement the light so you have a better idea of what oil pressure you do have.
hth
Sal