I put that in quotes because yes, I've seen it also result in an age bias and as I went from one side of the equation to the other, I spent some time evaluating what was and was not important to me as an employee.
About 15 years ago I came to the conclusion that "over qualified" was never a legitimate disqualifying disposition of a candidate. Simply put, if you are applying for a job that needs less skills than you bring and are willing to take the salary that is offered, how far 'beyond' the requirements you go is irrelevant. I asked a hiring manager at Google once if they would tell a sales guy "No I don't want the Ferrari at the same price as this Mazda Miata, its more sports car than I need to get around." Even if you never expect to challenge the top end of the sports car you probably won't turn it down. Similarly with employees, if you are up front with them about what the job entails and they are ok with it, who are you to say they will be "bored" or "twiddling their thumbs all day" ?
Answer is, you aren't. Hire them and get get a discount on skilz they are offering you. Your company will be better for it.