How long can beers age?

You can pull it off with the right beer. I suggest two bottles per table in case one goes bad? You can go 15, 25, 35, or 137 years with beer. (The 137 has happened. It isn't a joke.) Will it go sour after 15 years? If it goes sour, there was something wrong with the beer in the first place. Aging can be a crapshoot either way.

I suggest the following:
Dogfish Head World Wide Stout
J.W. Lees Vintage Harvest Ale
Alesmith Old Numbskull (lots of space on the bottle to sign)
Cantillon will work, but you may have a hard time finding that many bottles.

 

Agreed. JW Lee's Harvest, or most any English barleywine or old ale. A few English style American offerings might hold up, like Oak Horizontal, Mirror Mirror, Our Finest Regards. Anything truly American with the hops ramped up will be too much dead in 15 years from my experience (Hog Heaven, Bigfoot). DFH WWS, 120 can easily sit a decade, maybe more.

Belgian quads aren't a bad idea either. Abt 12, Rochefort 10, etc. Gueuzes will go the trip too as long as they're kept properly. Most anything bottle conditioned has several years available on it already, so pick something with big ABV and not a lot of additives and you'll be ok. Might not be great, but it won't fall apart and be awful.

 

This is a great question, actually. My first child is being born in August. Back story, when I was in Rehoboth Beach with my wife, we overheard a guy telling his son at DFH that he'd bought a bottle of the Olde School to share on the kid's 21st birthday (the kid was probably six). I always thought it'd be a cool idea to have a bottle of something with his/her year on it to share.

Any other (affordable) suggestions for some things that may last that long?

 

I did that for both my sons (2011 and 2013 vintages) with Fuller's Vintage Ale. Got 2 bottles for each year. They're cheap, so if it doesn't work...oh well. Should be fun to see how they turn out.

 

Why would the wine have to be that expensive?

I have a few 2011 and 2013 beers aside for when the two kiddos turn 21 for me to drink, easy to find cheap stuff, like WWS and 120, Olde School and a few other things for fun. Great idea. You can definitely find stuff that should last, but worst case wouldn't be overly expensive to get.

Did you want a variety or the same thing. In a way it'd be cool to do the same beer every year just to see how it turns out each year!

 

Ahh I didn't realize that about wine. I figured you can just get to drinking it whenever you want....with no crazy effects on it. (for the most part)

You should look for a case of World Wide Stout or even Bigfoot. That would be easy to find....as for people signing the bottles, they wouldn't be big enough, so if you are looking for bombers or 750s...I'd have to think a bit about what would be easy to find and relatively in expensive

 

aging wine is a lot like aging beer. It depends on the style. Bordeaux wines age very well. If BOTH of you enjoy wine more, then use wine. If you're both into beer, then use beer. Sours can absolutely hold up for 15 years.

 

I recently had a '10 WWS that was fantastic four years later and I love Olde School, so maybe those both are the way to go with the purchases. I think it's a good move, too, to buy the same things to possibly make observations like, "Wow, the 2014 WWS was great, but the '16 held up terribly."

 

The big gueuzes (need not be Cantillon) can hold on, sure. To get 10+ years out of anything else, go absolutely as big as you can get, some bottle-conditioned dark quad or imperial stout at >10%ABV. No guarantees with any of those, either.

What about a mix of beer for the lower numbers and and wine for the higher numbers? I don't think you have to do *that* much special to get wine to last. You might might have to spend that for some Premiers Crus but you could go a couple notches down the Bordeaux chain. Just make sure to check the corks every few years and recork anything loose or saturated. It could probably be done for not much more than the import price of a Cantillon.