Walker recently gave an interview to Right Wing News, in which he tried to align himself with conservative icon Ronald Reagan (a common thing for a GOP politician to do). Now he could have said the he admired Reagan and wanted to be just like him, and that would probably be accepted as true by most people. But Walker had to go further. He actually said he voted for Reagan.
The problem with that is that he couldn't have voted for Reagan, and he knows it. Walker was not born until November of 1967. That means he had just turned 13 when Reagan ran for president in 1980, and had just turned 17 when Reagan ran for re-election in 1984 -- and neither 13 nor 17 year-olds can vote in any state in this country.
Walker just flat out told a lie, evidently thinking that no one would do the math and expose that lie. And it was a silly and unnecessary lie, since those he was talking to would have happily accepted his desire to be like Reagan. As I said before, it's like Republicans have this compulsion to lie (even when it does them no good).
(The caricature of Scott Walker shown above is by DonkeyHotey.)