Answer: sixty

AnswerCrossword Clue
SIXTY

Semicentenarian's next milestone

SIXTY

A mile a minute

SIXTY

Threescore

SIXTY
Highest score possible with a single dart
SIXTY
Mile-a-minute speed
SIXTYIt's often done on highways
SIXTYFive dozen
SIXTYMaximum number of marbles at play in a Chinese checkers game
SIXTYThe smallest number divisible by the numbers 1 to 6
SIXTYSeconds or minutes numbers
SIXTYJust passing
SIXTYLimit, at times
SIXTYSpeed limit, at times
SIXTYSpringtime temperature
SIXTYRisky speed.
SIXTYNumber.
SIXTY...-four dollar question
SIXTYThree score
SIXTY"When I'm ... -four": Beatles
SIXTYNearing retirement age, maybe
SIXTYHighest score achievable by a single dart in darts
SIXTYBabe Ruth mark broken by Roger Maris
SIXTYSexagenarian number
SIXTYNumber Roger Maris beat
SIXTYThe new 40, they say
SIXTYBase of the Babylonian number system