Why? I can kinda understand the Alternate Breath Weapon having a prereq but doesn't scream it needs it.
Breath Weapon Burst doesn't deal any extra damage or anything just makes a breath weapon a targeted weapon so it doesn't kill it's allies. (For those dragons that play well with others.)
Hmmm, yea I could see that, except it takes no time at all for a dragon to reach an age category that has that much in ability. They do have the prereqs of being the Dragon type.
Personally, I would require Int over Con on the Breath Weapon Burst, this is a strategy weapon, and dumber dragons would probably not develop this one.
And the alternate breath weapon prereq works, keeps you from using fire to deal negative levels for shadow dragons.