Update 4:03 p.m.: Lautenberg announced shortly after this post went up that he will not seek reelection.

Sen. Frank Lautenberg's (D-N.J.) age is sure to be an issue if he faces a primary against Newark Mayor Cory Booker in 2014.

As of now, though, his age remains a complete mystery to most New Jerseyans.

A new Monmouth University poll shows that a whopping 46 percent of people in the Garden State think that the 89-year-old senator is in his 60s or 70s, while just 39 percent correctly state that he's in his 80s.

Sen. Frank Lautenberg (D-N.J.), right, with Sen. Bob Menendez (D-N.J.). (AP)

Interestingly, the poll shows just 34 percent of respondents say Lautenberg is too old to be an effective senator. That's far different from a Quinnipiac University poll from last month that showed 70 percent thought Lautenberg's age was more of a liability than a benefit.

Why the big difference? Well, the Quinnipiac poll actually told respondents how old Lautenberg was; Monmouth didn't. (Update: a reader also points out that the Q poll surveyed registered voters, while Monmouth surveyed all adults, which suggests former's sample is more politically aware.)

"The lack of concern over Sen. Lautenberg’s age is probably related to the fact that most voters have no idea how old he is," writes the pollster.

That's very true. In fact, among the sub-sample of voters in the Monmouth poll who correctly pegged Lautenberg as an octogenarian, 57 percent said he is too old to be an effective senator.

You have to think that after a lengthy Senate primary, voters would become quite aware that they would be voting for a guy who is 90 years old. Even if Booker doesn't make overt reference to Lautenberg's age, it's going to be hard to ignore the fact that Lautenberg's age would begin with the numeral 9.

And the fact that this is very much an issue for the people who are aware of it suggests it's very much an issue for Lautenberg.