The comedian came out guns blazing Monday night in his first gig of hosting the Comedy Central show anew ... and yes, he was ready to discuss the upcoming 2024 election -- diving head-first into the candidates (thus far), and taking aim at POTUS.

As you can see, Jon didn't hold back ... taking jabs at Biden for a recent slip-up where he mistakenly referred to the Egyptian President Abdel Fattah El-Sisi as the president of Mexico during a recent press conference.

He also called out Biden for, at times, not being able to recall basic details during his deposition regarding the Special Counsel report on his management of classified documents.

Now, JB's opponent wasn't let off the hook so easily -- JS also roasted Donald Trump ... playing a clip of DT's own deposition where he also couldn't remember stuff, quipping, "It turns out that the leading cause of early onset dementia is being deposed."

Stewart continued bashing the two for being too old ... pointing out they are well outside the age range for anyone who has run for the presidency in the country's history.

Jon roasted the hell out of both of them ... saying that while both might be "vibrant, productive or even capable," they were each also "stretching the limits of being able to handle the toughest job in the world."

Basically, he's saying that Trump and Biden should make way for new blood in politics -- especially now that they've both got their AARP cards, social security, and movie discounts.