What about 1 year? 2 years?
And don't start with the "Brady says he wants to play until 45" thing. He can say that, but we'll see what actually happens, both within and outside of Brady's control. (And for the record I'd love for Brady to play at a high level for 5 years, and said that even when JG was still with the team.)
What about his performance to date has suggested to you that he's going to fall off a cliff in the next 1-2 years? I know people like to say that the end comes suddenly with QBs, but that's not really true. Brett Favre was notoriously inconsistent from age 36 onward, he was just as bad at 36 as at 40. Manning was dealing with an injury that forced him to rework all of his mechanics and inevitably led into another injury that he couldn't recover from. Warren Moon had a pronounced decline at age 40, then rebounded at 41 and fell off the cliff again at 42.
Brady, meanwhile, has without exception been an elite QB for every snap he's played over the last decade-plus. There has been no sign of decline. So until there's a real, tangible sign of decline, I don't see any point at all in hand-wringing over the theoretical possibility that this time next year he might be a **** quarterback.
My stance on this has been pretty consistent throughout: I'm going to wait to see some real, meaningful indication of decline, and only
after that happens will I think it's reasonable to start putting a timeline on the remainder of Brady's career. People have been projecting the inevitable decline for 5+ years now, and they get it wrong every year. They'll get it right eventually, but they'll have been wrong 10 times before they were right. It's like Ron Paul predicting economic collapse every two years, or people who say the Spurs got old every offseason (I made a nice chunk of basically free money over the years betting the over on the Spurs win total every season). If you're wrong 10 times before you're right, then you weren't right at all.
The day we can definitively say Brady is in decline, then I'll be fine with this "1-2 years of Brady vs. 10 years of the other guy" talk, but since that hasn't happened yet I just don't see the point. It's highly likely that Brady has more years left in his career as a top-3 QB than Matt Ryan, Eli Manning, Phil Rivers and Carson Palmer had combined over their full careers, and again, projecting Garoppolo as a Matt Ryan / Phil Rivers caliber QB is pretty optimistic.
And **** it, even if Brady does decline over the next 1-2 years, that'll give Belichick/McDaniels plenty of time to draft and develop his replacement.