The band announced its farewell tour Monday, titled 'Peace Out' -- a 40-date slate that kicks off on Sep. 2 in Philly and runs through the end of January to finish in Montreal ... with a lot of stops in between, including their hometown of Boston.

The reason they're saying goodbye forever is two-pronged -- they wanna celebrate their 50-plus years together ... but, more importantly, they want to capitalize on their ability to jam together ... which Aerosmith candidly admits won't last forever, especially as they get older.

Joe Perry made a telling point ... "You never know how much longer everybody’s going to be healthy to do this," adding, "It’s been a while since we’ve actually done a real tour. We did that run in Vegas, which was great. It was fun, but (we’re) kind of anxious to get back on the road." Of course, he's referencing their recent Vegas residency.

The five founding members, who've all been there pretty much since the beginning, are all over the age of 70 ... with frontman Steven Tyler being the oldest at 75.

While everybody's still kicking/rocking -- as evidenced in their recent stint in Sin City -- Perry might have a point about getting in one last shot at what very well may be their last window to perform in tip-top shape. The Aerosmith guys have endured their fair share of health scares over the years, especially of late -- ST's bout of a mystery illness comes to mind.

A farewell tour for Aerosmith has been getting teased for years now, but it sounds like this could actually be the final time you can catch them live. It's unclear if they're going full international -- or if they're just sticking to North America.