In my example, is there a clever way to remove the dashes?

Question

This raises concerns because people who are 21 years-old and are now legally able to drink — but were born before the 15th of the month of their 21st birthday — will not be accounted for.

Answer 1

Commas will serve the same purpose.

This raises concerns because people who are 21 years old and are now legally able to drink, but were born before the 15th of the month of their 21st birthday, will not be accounted for.

Answer 2

I think you should bring "but were born... birthday" directly after "are 21 years old" because that's the concept it modifies.

This raises concerns because people who are 21 years-old but were born before the 15th of the month of their 21st birthday are now legally able to drink but will not be accounted for.

people who are 21 years-old but were born before the 15th of the month of their 21st birthday is one noun phrase

Answer 3

The em-dashes here separate a .clause which would ordinarily fit fairly well without any addressing. I assume that you originally used them for stylistic reasons -- I support this, by the way -- but they aren't strictly necessary. In fact, the sentence you give would be perfectly fine (grammatically) with no punctuation...

This raises concerns because people who are 21 years-old and are now legally able to drink but were born before the 15th of the month of their 21st birthday will not be accounted for.

...but it's a bit wordy and difficult to parse. Instead you might replace the dashes with commas for a lighter-handed feeling but much the same effect.

Answer 4

I'd group differently to tie together the age references (either side of the parenthesis):

This raises concerns because people who are 21 years old (and are thus now legally able to drink), but were born before the 15th of the month of their 21st birthday, will not be accounted for.