Hmmm...as long as the gap between CR and caster level isn't too great, we may be OK.
Still, looking at other true dragons at 12 HD or less, the caster level is usually 1st. That's an enormous difference.
I think I'd be more comfortable if we either reduced the caster level progression, doubled the HD at each age category, or just stuck with a robust spell-like ability progression.
The more I think about it, I think I prefer the last option, as it is closest to the original flavor, and keeps them realistic at HD for their sizes.
For what it is worth I like the robust spell-like ability progression.
Keep up the good work.