I've had bottled beer that was still good 18 months later. The key to stability is avoiding exposure to air, and to try and keep yeast and sediment out of the bottles. The pro's filter their beer through plates, screens, or other contraptions to get all gunk out of the beer before bottling. Home brewers can get filters, but they are expensive. Another technique is to cold crash -
http://www.brewersfriend.com/2009/04/18 ... rify-beer/. To avoid oxidation, what I often do is select a highly flocculent yeast (that settles to the bottom well), and skip racking to a secondary. This route saves time, but doesn't do great with preventing sediment 100%. If you do rack, make sure to select a secondary size that you can completely fill up to the neck. So if you ferment in a 6 gallon, rack to a 5 gallon. That keeps air away from the beer.
Heavier beers (like a barely wine at 11% ABV) will have more stability in the bottle and even flavor development over time. We have a 2008 barely wine that is still drinkable when we tried it a few months ago.
Dry hopping effects diminish after 6-8 weeks. When dry hopping drink sooner. Yum!
Maybe what you need to think about as well is a best after date. Beer is best after it conditions correctly, and this can take several weeks. Some yeast also need time to clean themselves up. Every time I have opened a bottle before 45 days after brew date, or before 4 weeks in the bottle, I've been disappointed. So, patience is the key to getting the most out of every bottle.