Wine or champagne as christening present?

I'm thinking of giving a decent bottle of wine or champagne, or maybe even a spirit, to my godchild-to-be for his christening that will age well. I'm imagining him opening it on his 18th or 21st, so I want something that will be quite special (and actually drinkable) after twenty-odd years. I don't know much about wines/champagnes/spirits so has anyone got any recommendations? I'm thinking of spending upto �100 now if needs be. Also, anyone know where I can go to buy something like this - I live in Reading and think Majestic may stock what I need (I need to buy other wine so don't have a problem with the quantity issue).