Background
The Japanese give regnal eras to each Emperors reign, so the Showa Era ("Enlightened Peace" or "Radiant Japan") was the reign of Emperor Hirohito from December 1926 to January 1989. Any wrestler who trained and was active during this era, is known as a "Showa-Era Wrestler".The Showa Era was followed by the Heisei Era (8th January 1989 - 30th April 2019). At the time of writing, Japan is currently in the Reiwa Era (1st May 2019 onwards).
Wrestling terms
"Showa Era Wrestler"
Masa Kitamiya is often referred to as wrestling "Showa Era" style, although he himself trained during the Heisei Era. To wrestle "Showa Era" style means that his style is reminiscent of an older time in wrestling, the more classical style that belonged to his senior, Masa Saito, which would not have looked out of place in the Giant Baba era of All Japan.
The majority of Noah are Heisei Era wrestlers, while the trainees in the dojo will be Reiwa era wrestlers. Each era is marked by its own style; Showa Era encompass the veterans, Heisei era are the current product, with Reiwa in Noah yet to be seen, but I would imagine that with a varied mix of teachers, they will encompass both styles while bringing their own in.
Trivia
Although Masa Kitamiya is the "Showa Era" style wrestler, he never actually wrestled in the Showa Era, having been born in 1988 the year before Hirohito died. However, Yoshinari Ogawa has wrestled in all three eras having debuted in All Japan in 1985 (Showa), where he remained until 2000 (Heisei) and is still active there in 2020 (Reiwa).