Ash Wednesday and Good Friday are ‘Days of Fasting and Abstinence’, which means that:
All Catholics age 14 and older are required to abstain:
“The law of abstinence forbids the eating of meat, but eggs, milk products, and condiments made from animal fat may be eaten. Fish and all cold blooded animals may be eaten, e.g., frogs, clams, turtles, etc.”
All Catholics age 18 and older, but under the age of 59, are required to fast:
“The law of fast prescribes that only one full meal a day is taken. [In addition] Two lighter meals are permitted to maintain strength according to each one's needs. Eating between meals is not permitted, but liquids, including milk and fruit juices, are allowed.” (Pope Paul VI, Paenitemini, 1966, (the current law)).
Fasting and abstaining are important ways for us to unite ourselves with Our Lord’s 40 days in the desert. Christ fasted, the Early Church fasted, and Christians down through the ages have fasted. All fasting helps us grow in spiritual self-discipline to prevent future sin and helps us offer up penance in reparation for our past sins. Abstaining is a mild form of fasting in that we deny ourselves a particular pleasure, namely meat. By observing these days as communal fast days we join with the whole Church across the world in acknowledging the importance of these particular days. Children and the elderly are strongly encouraged to fast even when the law does not bind them (Canon 1252), or to offer up some other acts of self-denial.
And in case you were wondering… Canon Law specifies: If your 14th or 18th birthday happens to fall on a ‘day of fasting and abstinence’ then you are not required to fast/abstain. However, if your 59th birthday falls on a day of fasting then you are bound by the law of fasting; the obligation ceases on the next day. Sorry.