In 2004, Barry Bonds hit 45 home runs in the season in which he turned 40 years old. That, however, included only 20 homers after his actual 40th birthday. Darrell Evans, in 1987, hit 29 of his 34 homers after his 40th birthday in May of that year giving him the most over-40 homers in a season.
Much less suspiciously, Craig Biggio has an excellent chance this year to set the over 40 record for doubles, and a possibility of getting the over 40 plunk record.
With 16 doubles already, Biggio could break the all time single season - 67 by Earl Webb in 1931 - but he would have to keep his current pace through the rest of the season. The over 40 doubles record is 35, set by Sam Rice in 1930 at the age of 40. Paul Molitor hit 41 doubles in 1996, but didn't turn 40 until August 22nd of that year. Only 9 of those 41 doubles were post-40 for Molitor.
The single season plunk record for a player over 40 is 19, set by a 42 year old Deacon White in 1890, 9 years before Aspirin was patented.