The New England Patriots have played in five Super Bowls -- winning three -- since they drafted quarterback Tom Brady in the sixth round in 2000. They also have eight division titles in that span, and Brady and coach Bill Belichick recently became the winningest quarterback-coach combo in NFL history.

But all of that comes to an end when Brady retires.

Brady, who turns 35 in August, says he wants to play in New England until he's 40. That is great news for the Patriots, because they will struggle the second the future Hall of Famer hangs it up.

Things that have become foreign to New England the past dozen years will become routine again. New England will have down years and miss the playoffs -- just like everybody else. The Patriots won't survive various injuries -- just like everybody else. The Patriots also will run through a few quarterbacks -- just like everybody else.

On Wednesday, ESPN.com examined potentially dominant teams in 2015 . At that point, I think New England's easy run over the AFC East will be a thing of the past.

Here are four reasons New England will struggle in the post-Brady era:

No. 1: Patriots won't immediately find Brady's replacement.

Brady's story is once in a generation. He's a former sixth-round pick who slipped through the cracks to become one of the top five quarterbacks of all time. Brady had the drive and “it" factor to become the greatest player in franchise history. Brady often is compared to Joe Montana, because they share a similar story about 20 years apart.

The chances of New England finding another Brady anytime soon are slim.

Will Ryan Mallett be ready to take over for Tom Brady when the future Hall of Famer is ready to hang it up? Stew Milne/US Presswire

Patriots fans will scream that Ryan Mallett is a future franchise quarterback. But how does anyone really know, considering the 2011 third-round pick hasn't thrown an NFL pass?

What about Brian Hoyer? The undrafted quarterback has shown small flashes but certainly not enough to warrant Pro Bowl status. The drop-off going from Brady to 99 percent of other quarterbacks will be steep.

Even if Mallett or Hoyer turns out to be a viable starting quarterback, neither will be nearly as good as Brady. Is Mallett or Hoyer a future Hall of Famer? Probably not. Will either quarterback perennially make the Pro Bowl? Not likely.

New England has been able to overcome poor defense, injuries and at times average receivers to still be competitive. Brady was great enough to carry the Patriots through various weaknesses. That no longer will be a luxury in New England. It will be much harder to get everything right with other areas of the team, especially if the quarterback position is in flux.

No. 2: The offense is old.

Brady is turning 35 in August. No. 1 receiver Wes Welker is 31. Starting receiver Brandon Lloyd is 30. Longtime left tackle Matt Light just retired this offseason. Guard Brian Waters might follow, if not this year, then soon after.

When Brady is gone, it's likely all these important offensive pieces will be gone as well. A Patriots offense without Brady, Welker, Lloyd, Light, Waters, etc., means New England is virtually starting over in a few years.

The Patriots still have a couple of young stars in tight ends Rob Gronkowski and Aaron Hernandez. But consider this: One tight end probably will bolt in free agency. Both Gronkowski and Hernandez -- two of the top five players at their position -- have rookie contracts set to expire in two years. Both will be looking for huge paydays, and New England can't do that with two players at the same position.

New England most likely will throw the money truck at Gronkowski, perhaps making him the highest-paid tight end, and let Hernandez walk. Brady also will be 37 and possibly retired or on his last legs by the time both tight ends will look for extensions. Returning to New England's offense long term won't be as attractive two years from now for a pending free agent such as Hernandez.

No. 3: Sun is setting on Belichick.

Belichick just turned 60 years old. How much longer will he coach the Patriots?

He has coached in the NFL in some capacity for 37 years. He is approaching his fourth decade in the league.

Even head coaches have a shelf life. Belichick currently is the NFL's fourth-oldest head coach behind Tom Coughlin (65) of the New York Giants, Romeo Crennel (64) of the Kansas City Chiefs and, by a few months, Chan Gailey (60) of the Buffalo Bills. Perhaps we are also witnessing the last few years of Belichick roaming the sidelines.

A good debate topic in New England would be who contributed more to the Patriots' dynasty the past dozen years: Brady or Belichick? Both are Hall of Famers. But in my opinion, Brady's development and dominance at quarterback are stronger factors in New England's success. Belichick would not have won all those games, division titles and championships in New England with shoddy quarterback play. Brady remained dominant and kept the team afloat, even when Belichick struggled coaching the defense, which is Belichick's specialty.

No. 4: The rest of the AFC East will catch up.

I often call the AFC East the "Brady and Belichick division." They're the great equalizers who keep the Patriots on top.

But without Brady in a few years, and perhaps Belichick, all four teams are back to an even playing field. Who will be the top quarterback in the AFC East when Brady retires? Ryan Tannehill? Mark Sanchez? Tim Tebow? Someone else?

Maybe all four teams will have average quarterback play. That means the Patriots, New York Jets, Bills and Miami Dolphins must rely on other areas to be successful and win the division.

Can the Patriots rely on their defense to lead the way? Not right now. Not even close. New England is in no position to overcome poor quarterback play, and that probably won't change overnight.

I expect Brady to play at least two more years (2012 and 2013) at an elite level. He might opt to play beyond that. But after age 37, there's no guarantee Brady can continue to take the physical pounding and play at the high level to which we have become accustomed. We've already seen nagging injuries bother Brady more than ever over the past couple of seasons.

Brady is a special talent the organization probably will never see again. So enjoy the success now, Patriots fans. New England will come back to earth and be an ordinary team again in three to five years.