It's my understanding a big mead could make it to 10 years but IDK about 20. Some wine styles age better than others, but I'm sure there's a wine style you could make that would peak flavor at 20 years (talk about a killer gift!)
I read somewhere that the Carlsberg Vintage no. 3 should age well for 50-100 years (???!!! it even says so on the bottles, reportedly!) -- http://www.carlsberggroup.com/media/News/Pages/PR_04_04032010_Vintages.aspx
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so if you have the facilities to do something like this then maybe it'll age fine for 21 years? From what I've read they pushed this beer to 15,8 % using several yeast additions. I don't know other details except what you find by googling.
The other posters are probably right in suggesting mead, wine or port!