Too much damage and immediate-level flexibility on the breath weapon. Have the character choose which type of breath weapon from a standard selection when they Focus, and set the base damage ratings as for Very Young dragon; if they already have a breath weapon of that type, increase its DC by +2, its range by 50% and its damage by 2 or 4 dice depending on whether it's a half-progression or full. At levels 4/7/10* give them either 2 dice or 1 die of damage, again depending on the breath weapon's normal growth rate (i.e. +1d6 for a white breath weapon, +2d4 for black, etc)
I seem to have missed where they either receive, or become immune/resistant to, Frightful Presence. An oversight, I'm sure
At least, it seems appropriate that there be a Focus ability which imposes a Frightful Presence and makes them immune to that of "other" dragons, though you might stipulate that they choose a dragon type. :)
Oh, and the proper plural of "focus" is "foci" :)
Edit - you should probably change the skill requirement to 13 (level 10 equivalent). Tough to take 10 levels in a PrC after needing 11 to qualify, without going epic. And while I could be wrong, I'd thought dragons were classed under "arcana" rather than "nature," no?
*if a dragon needs 3 hit dice to increase its breath weapon, then so does this class. :)