Tier 0 are ancient dragons, an unattainable tier, there are only 5 of them
tier 1st and are disciples of the ancient dragons, who live several thousand years, are immortal and have elemental runes, usually really powerfull
Tier 2 are descendants of ancient dragons, and they are always wyverns, and they not only learn to change into dragon form from childhood but also have powers very early and often have element runes from birth, so they can be immortal, but it's not a rule
Tier 3rd are like disciples of the Ancients or 1st tier who are not very experienced, have powers and also turn into dragons
Tier 4th are students of 2nd or 3rd tier, and usually they are not powerful enough to use elemental powers and change into a dragon so they kinda only have one of those to choose from, usually it's just powers without changing
There is also tier 5, which as such is not one tiers, because if someone has been exposed to elemental runes for a long time, but not having it directly can use elemental powers