First off despite the naysayers who beleive you can't age a beer for that long, evidently Charlie Papazian can. With proper storage.
In the Dec 07 Zymurgy Charlie Papazian reviewed bottles of homebrew going back to the first AHC competition that he had stored, and none of them went bad, some had not held up but most of them he felt were awesome...We're talking over 20 years worth of beers.
Since nothing pathogenic can grow in beer, there's no worry needed about getting sick from them. All that can happen is that they may not have held up over time.
This is a great thread about one of our guys tasting 4-5 years of his stored brew.
https://www.homebrewtalk.com/f14/revisiting-my-classics-160672/
Beer's like wine, a lot of them improve with age....That's why stone has "vertical epic" with vintage, and people have vertical tasting parties
I made a beer that won't even be opened before 5 years go by on Sunday.
https://www.homebrewtalk.com/f12/he...emorial-5-year-aged-barleywine-recipe-195096/
The people who are suggestion you aim for a Utopia clone, are really not that off base. If you want to make a special beer and age it, then a super barleywine IS the way to go. Something big and heavy where some oxydation and sherry notes will be ok.
If you don't want to make a 5 gallon batch then make a 2.5 gallon batch and even if it is not spectacular it still will have meaining. Or even a gallon batch with only a few bottles.
Here's the two uber threads on brewing utopias..they are fun reads even if you don't brew one.
https://www.homebrewtalk.com/f12/way-way-way-over-top-sam-adams-utopia-clone-91463/
https://www.homebrewtalk.com/f12/way-way-way-over-top-sam-adams-utopia-clone-2-a-136326/
There's no harm in trying. And if you do a nice bottle, with a great label, and wax covered cap, even if the beer doesn't hold up it will have special meaning.
You can also make a 5 year down the line as a back up, but still even if the bottles are never opened on the 20 year ones beyond the one that you realized it didn't turn out.
You will still have something special.