E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
It was once believed that 7 and 9, with their multiples, were critical points in life; and 63, which is produced by multiplying 7 and 9 together, was termed the Grand Climacteric, which few persons succeeded in outliving.
There are two years, the seventh and the ninth, that commonly bring great changes in a mans life, and great dangers; wherefore 63, that contains both these numbers multiplied together, comes not without heaps of dangers.Levinus Lemnius.