To falsify numbers or one's age to one's advantage; an idiom meaning to cook the books or lie about age (colloquial).
彼は試験の点数をサバを読んでいる疑いがある。
There's suspicion that he has fudged his exam scores.
若く見られたいから年をサバを読んだと言っていたよ。
He said he lied about his age because he wanted to look younger.
会計チェックで売上がサバを読まれていたことが判明した。
The audit revealed that the sales figures had been falsified.