"Hyakunen hayai ze!"
This is a common boast in shounen anime, declaring that someone is X amount of years too early to even consider facing their opponent.
Is this a long-lived reference to an older anime's catch-phrase? (in a similar vein to "You are already dead" from Fist of The North Star)
The catchphrase comes from character Akira Yuki from the Virtua Fighter series, and was popularized as a seiyuu meme (basically a meme associated to a voice actor) related to famous voice actor Shin-ichiro Miki.
Akira is the main character of the Virtua Fighter series, and his catchphrase was used in every game of the series, starting with the first opus in 1993 for arcade.
十年早いんだよ！
It's ten years too early! [for you to win against me]
History of jyuunen hayaindayo! (youtube)
After the success of the first game, a Virtua Fighter anime is produced in 1995, with Shin-ichiro Miki acting the voice of Akira. Since then, Shin-ichiro Miki voiced the character in every installment of the series.
The catchphrase gained popularity and became an easter egg related to Shin-ichiro Miki.
Notably, Shin-ichiro voiced in 1996 Ryuusei Date, the main character of the game Shin Super Robot Taisen (Shin Super Robot Wars). In this game, Ryuusei says the famous sentence. With the success of the Shin Super Robot Taisen game, the catchphrase will gain even more momentum afterwards.
In the following games of the Robot Taisen series, Ryuusei said the catchphrase again, and, starting with Super Robot Taisen α (2000), Ryuusei got more confident and started adding years to the sentence:
百年早いんだよ！
It's 100 years too early!
Ryuusei didn't stop there, and a 1000 years, then a million years variation ensued in the following games. Eventually, Ryuusei got back to 10 years in the more recent installments of the Super Robot Taisen games.
At this point in time, it is a nod to Shin-ichiro Miki to mention the catchphrase, and it is interesting to note that the seiyuu played a part in most major shounen anime, even though most are also minor roles.
It actually comes from Fist of the North Star ironically, The fight between Kaiser and Shachi which released in 1987, Years before Virtua Fighter was even a thing.
