Maybe 21 <=> 100 is just the easiest cross over point between the two age scales. Its easier to remember than 18 <=> 85.5 or 16 <=> 76.2 so that’s where they start. They arrive at an equivalent age of 15 and deem that to young. No information was ever given about what the age of legal drinking is. Just that it is older than 15.
Also dwarven ale might be straight schnaps with 80% alcohol for all we know. Don’t want 16 year olds drinking that even if you think beer is fine.
Maybe 21 <=> 100 is just the easiest cross over point between the two age scales. Its easier to remember than 18 <=> 85.5 or 16 <=> 76.2 so that’s where they start. They arrive at an equivalent age of 15 and deem that to young. No information was ever given about what the age of legal drinking is. Just that it is older than 15.
Also dwarven ale might be straight schnaps with 80% alcohol for all we know. Don’t want 16 year olds drinking that even if you think beer is fine.