A pirate's impressiveness and first-impression strength is usually dictated by the bounty he or she earns. Therefore, the higher the number, the more fame and respect the said pirates receive. Any rookie pirates who manage to receive a bounty of over 100,000,000 before they enter the New World are considered to be impressive, as it marks that said rookie has committed criminal acts of catastrophic degrees. However, once past the "Paradise" half of the Grand Line, bounties of around 100,000,000 are considered common and even weak.
While bounties of 300,000,000 are highly impressive, a pirate with one can still be considered a rookie. A pirate may ultimately shed their rookie status after several years of regular pirating activity.
One year before the start of the series, Cavendish gained a high reputation among the rookies, with a bounty of 280,000,000. A year after he earned his bounty, the Worst Generation's arrival overshadowed him, causing him to develop a grudge against them.
Two years before the current storyline, eleven Super Rookies arrived at Sabaody Archipelago almost simultaneously. Collectively, they are known as the "Eleven Supernovas" (11人の超新星,Jūichinin no Chōshinsei?). These eleven, alongside Blackbeard, were considered to be the Worst Generation (最悪の世代,Saiaku no Sedai?) to ever come to existence, due to their individual actions bringing great (or terrible) changes to the world, leaving deep and lasting impacts.
One year after the Worst Generation's rise, at least another Super Rookie earned his fame: Bartolomeo the Cannibal, wanted for killing innocent civilians. He is hated and despised by many people, pirates and citizens alike.
In the current timeline, came at least two more: Caribou and his brother Coribou, both well known for killing Marines. Though both brothers were impressive in their own rights, neither of them were comparable to the Worst Generation.
Bellamy once held a similar title: he was known as the "Big-Time Rookie" (大型ルーキー,Ōgata Rūkī?), due to his bounty being at a moderately high 55,000,000, something his crew and Mock Town found impressive and noteworthy.
It should be noted that after the two-years timeskip, his bounty indeed went over 100,000,000. However, by that time, it is unknown if he is still considered a rookie.
In the anime Shanks calls Ace a Super Rookie during their meeting. However, this did not happen in the manga and Ace's starting bounty is currently unknown.