The answer can vary sooo much from individual to individual. Some are still very small at 3 months while some are enormous, so if I told you that 24 grams would be an appropriate weight, for example, it may only be true for a small percentage of veileds of the same age.
If you post a photo we can help you tell if he's looking good, if you want a second opinion. But usually, as long as my babies are gaining weight from week to week, their bodies look full, and their little fat reservoir areas look good, then I'm not worried about how they compare to others their age.