New Jersey Sen. Frank Lautenberg (D) turned 89 this week. And, Newark Mayor Cory Booker, who is preparing to challenge Lautenberg in a Democratic primary next year, has already made clear that the the incumbent's time may have passed.

With that as a backdrop, this tweet on Wednesday caught our attention:

The tweet suggests that Lautenberg's advanced age might well be prohibitive to his chances of beating Booker  --  or anyone else -- in next year's primary.

In fact, though, if you look at all the senators who have lost re-nomination over the past 40 years, the average age was very much in line with the average age of the Senate.

Here are the 15 who have lost their party's nomination over the past four decades:

The average age of these senators is 63.2 years old. The average age of the last Congress was 62.2 years, according to the Congressional Research Service.

In addition, Lautenberg already turned aside a primary challenge from Rep. Rob Andrews (D-N.J.) in 2008 when he was 84 years old, and now-former-senator Daniel Akaka (D-Hawaii) beat then-Rep. Ed Case (D-Hawaii) in 2006 when Akaka was 82.

Now, that doesn't mean that advanced age is helpful. Indeed, many senators who are among the oldest in the Senate have the most incumbency built up, which makes them less likely to be primary targets in the first place.

But a look at the names above is instructive. The lion's share of the members who lost had ideological differences with their party's base (Lugar, Specter, Murkowski, Javits, etc.) -- something Lautenberg doesn't really suffer from.

But even knowing that, polls show that many Democrats in New Jersey say it's time for somebody new, and age may be a contributing factor to that. We live in an age of significant unhappiness with Washington, in which having been a senator for a long time isn't necessarily a feather in the cap.

In fact, a Quinnipiac University poll released today showed a whopping 70 percent of New Jersey Democrats say the biggest effect of Lautenberg's age is that it would make it more difficult to do his job, while just 24 percent said it was a net benefit because he's more experienced and wise. Those are remarkable numbers, even if voters aren't necessarily saying, 'You're too old.'

And, Lautenberg would be wise to remember that the three oldest senators who have lost primaries in recent decades all came in the last two elections -- Bob Bennett in Utah, Dick Lugar in Indiana and Arlen Specter in Pennsylvania -- and Lautenberg will have a decade on all of them by Election Day 2014. We quite frankly haven't seen a nonagenarian senator face a real primary in recent years, so it's unclear how his age might play out.

It's unlikely that Booker would make direct use of Lautenberg's age as an issue, but it would definitely be a major subplot of the race.

Update 1:21 p.m.: This post initially left out Lieberman's 2006 primary loss. Lieberman wound up running as an independent and retaining his seat. The numbers above have been updated to reflect Lieberman's inclusion.