Baseball Age (1889)

“Few persons know definitely how old [John Montgomery] Ward is. I do not, but I am not far off in placing it at 33, although his baseball age is given as 28.” W.J. Harris, Wilkes-Barre Sunday Morning Leader, March 10, 1889, p6 (Also appeared in other papers)

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1901. “I was 39 according to my base ball age, when I quit, but I kept the date of my first birthday a secret.” (Cap Anson, quoted in The Sporting News, November 9, 1901. [Peter Morris]