Yeah, "racial Hit Dice" is the more widely-used method. Let's use that.
It sounds like the majority prefer 1 min/age category for the breath weapon.
Updated.
Added a description, flavor text, and tactics.
Let's stick with the brass CR progression.
I don't really see a need for a subtype on these.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.