how long does beer in a bottle (unopened) stay good for at room temp.?

All depends on the type of beer...

Poor Quality: Cheap macro lagers like Bud, Miller, Coors and the like are best consumed fresh... About 3 months from bottling. 3-6 months they are still drinkable but will not taste fresh and carbonation may be lost. 6-12 months the drink will generally begin to become pretty nasty. Beer is probably the only food that even when it is "spoiled" it is still consumable and won't harm you. It may be nasty and make you want to throw up... but it won't kill you.

Good Beer: Bottle conditions, secondary fermentation, high ABV... Quality beers from some American micro brewers and imports form all of the world... Not all imports! With InBev controlling much of Europe's beer anymore it isn't any higher quality than its American counterparts. Anyway, craft beers can generally be stored and consumed for decades.

My hobby is collecting beer and cellaring (aging) it. Last weekend I had a 2002 and a 2003 Aventinus from Germany. For New Years I had a 15 year old Thomas Hardy's Ale. The fun part about it is taking notes when you try it fresh and then comparing them to the aged version. Some get better... others not so much.

I am sitting with a veteran beer brewer right now reading the answer to the question posed and we are currently drinking a 20yr old (conservatively) beer he brewed.

The beer is mostly likely a Coopers can brew and looks like it is "ale' or something similar.

I am sure the beverage will have the desired effect and that we will enjoy a convivial evening as a result.

Happy brewing

Clive and Harold the Brewer.