I have always known that we are supposed to fast on Ash Wednesday and Good Friday if we are between the ages of 21 and 59. The thing I’m confused about is how the rule applies when you are exactly 59-years-old and won’t be 60 until after Easter. Sometimes I read that 59-year-olds are supposed to fast, and sometimes I read that when you have reached your 59th birthday, you are excused from fasting.
Here’s the rule from the Code of Canon Law (1983):
The law of abstinence binds those who have completed their fourteenth year. The law of fasting binds those who have attained their majority, until the beginning of their sixtieth year. Pastors of souls and parents are to ensure that even those who by reason of their age are not bound by the law of fasting and abstinence, are taught the true meaning of penance (canon 1252; emphasis added).
If you count from birth, the first year is counted in months. The second year is counted as year one. This means that the beginning of the sixtieth year is a person’s fifty-ninth birthday. By the same token, it also means that someone who has “completed [his] fourteenth year” has just turned fourteen years old because year thirteen is counted as his fourteenth. It’s this same principle that counts the 1900s as the twentieth century. So, someone begins to abstain at fourteen, begins to fast at his majority, and is excused from fasting on Ash Wednesday and Good Friday on his fifty-ninth birthday. In your example, a person who is already fifty-nine on Ash Wednesday is excused.