Climb 20 or 30 is ok.
Climb instead of Jump in class skills is fine, too.
And Cleon's right on the gizzard AC.
Had some technical issues so I couldn't join in for the rest of the bestial dragon talk, but now I'm back. Some quick impressions on the hawkdragon:
- Seems like a small critter; it should only be modestly-sized at great wyrm.
- It ages rapidly, maybe as fast as the rattelyr in Shining South.
- Flying maneuverability is high, not below average perhaps. Plus it makes good use of the dive rules for flying. If it has an elemental subtype Air is an obvious choice.
- It seems to have a form of protection from arrows ability.
- A nice stinking cloud breath in a spread. If 2/day is too limiting we can just increase the rounds between breaths from 1d4.
- No spellcasting abilities.
I like giving them Jump as a class skill, I just think they should have Climb as well.
Yes, that's pretty much what I was thinking.
The main question is do we really need to give these little darlings with age categories?
I would just stat them as a 2HD Small or Tiny Dragon, using the SRD's Pseudodragon and Hawk for inspiration. Their Intelligence of Low-Average cover an Int range from 5 to 10.

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