How long is ok to leave bottled?

My friend, “assistant brewmaster”, is a senior in college on the east coast and we live in Oregon. We brewed a small batch before he left for school this semester, but he wasn’t able to taste any of it. He won’t be back until Christmas break, mid-December.

How long is too long to leave bottled? Are there any adverse effects of leaving a bottle of it for him upon his return to savor the fruits of our labor?

Depends upon the abv and the hop ibu level. More than likely, it will be fine, yet different than fresh beer. Cleanliness has a lot to do with it as well. I had a co-worker go to my old bosses house last year to be offered a beer that I made for him 2.5 years earlier. It was a blonde ale and it was very good still.

It’s ~4% ABV. Really low IBU. Just the American Wheat extract kit.

I recently tried a bottle that I had saved from my first foray into brewing. The beer was a big stout, and over 16 years old. It was incredible! I also have a pale ale from the same year. I don’t expect that one will be so good.

As others suggest, it depends on the type and strength of the beer, as well as how carefully it was packaged and how it was stored.
Two or three years or so ago, I opened the very last bottle of a rather hefty Scotch Ale I brewed in 1994.
Tasting it made me wish that I had saved the entire batch to enjoy now.
I was seriously amazed.

From the sounds of it, this beer will be fine by December, assuming good brewing practices, sanitation and fermentation.