I believe these are the numbers you're looking for:
Newbie = 1-49 posts
Hatchling = 50-299 posts
Juvie = 300-749 posts
Sub-Adult = 750-1499 posts
Gray-Bearded = 1500-2999 posts
Extreme = 3000-4999 posts
BD.org Addict = 5000-9999 posts
BD.org Sicko = 10,000 posts and up