What will cause oil to age prematurely?

I have a major inconsistent oil leak somewhere. I just did an oil change 3 weeks ago and am having to add a Qt per week. But the oil already looks like old oil. Is this a sign of a major problem? I haven't taken a good look at the leak either. its inconsistent. Nothing will come out for days at a time and then in a few hours half a qt or more will bleed out somewhere around the oil pan... and then there are times its a steady trickle from the same area. i know my temp isn't getting too high, although i don't have a guage, i know if the temp is okay just by how it smells. I keep putting new in there so it should look new but it looks old everytime i see it on the pavement or on the dipstick. ...its a 383 stroker thats got... maybe 30k miles since rebuilt.