Most dragons have been around in Kaelaross for eons - since elves can remember, at least. These dragons are
There are six main species:
White Dragons live in arctic and high mountains where there is snow and ice.
Black Dragons live in swamps and also underground
Green Dragons live in forests and jungles
Blue Dragons live in deserts and wide open plains
Red Dragons live in mountains and hills
Gold Dragons live in any habitat, including among humans.
All species have three main stages of growth - small, large and huge. These are generally a matter of age, not lineage. If you have the Rules Cyclopedia or Companion rules, then use the stats there. Otherwise small dragons use normal hit dice and damage, large dragons have 1.5 x normal hit dice and damage and -2 bonus to AC, while huge dragons have double the normal hit dice and damage and -4 bonus to AC. Obviously DMs are encouraged to adjust stats as they see fit.
Small dragons are relatively young (less than a century old), while large dragons are between one and five centuries old. Huge dragons are more than just big monsters - they are powerful forces that shape nations and landscapes, and can destroy populations. While small dragons are often unintelligent and animalistic, large dragons are cunning enough to acquire followers, guards and servants. Huge dragons are intelligent enough to either dominate hundreds of lesser creatures or else form alliances with powerful groups. As they acquire treasure, they may use this treasure to bribe or hire agents of other species, and fear and awe are also powerful motives - an ancient dragon who is wary of adventurers trying to steal his treasure may well have one or more spies in towns near his lair where adventurers would gather before an expedition. The same dragon may well have an agreement with tribes in the wilderness near its lair, while Charm Monster is a very useful spell if the dragon can learn it.
There is also considerable variation within each species, and were it not for a combination of academic study and certain subtle similar features, one might suppose there were far more species than there actually are. As it is, crossbreeding among these variants produces the base type. Cerulean dragons can breed with Ultramarine dragons to produce "normal" blue dragons, and Crimson dragons can breed with Sanguine dragons to produce "normal" red dragons.
Variants of red dragons are discussed here
Variants of blue dragons are discussed here
Variants of green dragons are discussed here
Variants of white dragons are discussed here
Variants of black dragons are discussed here
Some dragons have emerged from the Chaos Portals created during the Summoning, and as such can be found near, or even as part of, the armies of Chaos. Such creatures, regardless of their species or variant, are always chaotic and malevolent towards lesser creatures.
Known dragons of Kaelaross include:
Jadefury of the Talloak Forest and her family
Red Dragons (presumably small ones) are rarely found in the Godsblood Hills
Green Dragons (again small ones) are occasionally sighted in the Shorgan Forest
Small and large red and blue dragons are found in the Twisted Hills