In Interstellar, do people age while in cyro-sleep?

When Brand and Cooper return to their ship from Miller's planet, Brand sees the aged Rommily and says 'why didn't you sleep?' Later, on Mann's planet, Dr. Mann says he didn't specify an end date the last time he went into cryo-sleep.

Would Dr. Mann have eventually died of old age in cryo-sleep, or would he have stayed the same age? If Rommily had been in cyro-sleep for the 23 years that passed (relative to him) would he have stayed the same age as he was when Brand and Cooper returned?