Forget the Tom Brady-playing-until-45 debate ... Melvin Gordon says there's a GRIP of NFL QBs who can play to that age -- including his teammate, Philip Rivers!!
The Chargers superstar told us it's really not that hard for dudes like Brady, Rivers, Drew Brees, Matt Ryan and Russell Wilson to play forever ... 'cause they're studs who don't ever get hit like running backs do.
"I feel like those guys ... they quit when they want to, man," Gordon told TMZ Sports.
"As long as their arm's working, and they feel like they can throw and they can be in there, there's going to be someone that want them."
For the record ... the oldest QB to ever start a game was the Falcons' Steve DeBerg at 44 years and 279 days old.
If Gordon wants to see his boy Rivers break that mark ... there's only about 3,000 days left to go.