No the character just confirms that an equivalent age of 15 is too young. 21 is just the baseline age they use to do the calculation, because it lines up with 100 years in elf years. But the bartender wouldnt have to do the second part of the calculation at all if the drinking age is 21. It could easily be 16 or 17 and the elf would still be too young.
Which is exactly what the character is doing
No the character just confirms that an equivalent age of 15 is too young. 21 is just the baseline age they use to do the calculation, because it lines up with 100 years in elf years. But the bartender wouldnt have to do the second part of the calculation at all if the drinking age is 21. It could easily be 16 or 17 and the elf would still be too young.