So I wanted to follow up on my response. I went home and checked my notes, my last Oatmeal Stout (JZ's version) I brewed on 10/2- bottled 10/23 (3 weeks) and drank one last night 11/5 (2 weeks) since I had never tried it younger than 7 or 8 weeks. Aside from my cellar being at 58-60 degrees and taking longer to carb the beer was fantastic. I was quite shocked. I not saying that you should drink it early but you should try one earlier to see how it progresses. Mine tasted like a finely dark roasted coffee with chocolate cream. It was so silky smooth and intense compared to the 7 or 8 week stuff. I was blown away by how drinkable it was at that age. It was very roasty as expected but just awesome.
Last NHC I entered my oat stout that was a year old and it got 4 points higher in the second round than the "fresher" batch did. So if you are clean with your bottling you can keep it for at least that long.