The original editor of Gintama at Weekly Shonen Jump revealed the true age of Gintoki last night during a special live-stream for the Gintama: THE FINAL anime film.
As of February 7, 2021, Gintama: THE FINAL has sold 1,019,001 tickets for a total of 1,415,817,100 yen (US$13,418,032), making it the second-highest-grossing animated Gintama film.
This means during the events of Gintama: THE FINAL, the leader of Yorozuya is 29 years old.