Dragons would have longer natural lifespans than human beings, certainly -- but given that so many of them are involved in wars, a good many of the Targaryen dragons did not live out anything approaching a natural span, but died "young" by violence. This was especially true during the "Dance of the Dragons," where both sides used dragons in battle against each other.

There will be more information on the Targaryen dragons in future volumes, but I'm not certain I'll go so far as to do a dragon geneology. Thanks for the suggestion, though.