"We can think of Lent as a time to eradicate evil or cultivate virtue; a time to pull up weeds or plant good seeds. Which is better is clear, for the Christian ideal is always positive rather than negative." -Archbishop Fulton Sheen
Ash Wednesday and Good Friday are obligatory days of fasting and abstinence for Catholics. In addition, Fridays during Lent are obligatory days of abstinence (no meat).
For members of the Latin Catholic Church, the norms on fasting are obligatory from age 18 until age 59. When fasting, a person is permitted to eat one full meal, as well as two smaller meals that together are not equal to a full meal. The norms concerning abstinence from meat are binding upon members of the Latin Catholic Church from age 14 onwards.
If possible, the fast on Good Friday is continued until the Easter Vigil (on Holy Saturday night) as the "paschal fast" to honor the suffering and death of the Lord Jesus, and to prepare ourselves to share more fully and to celebrate more readily his Resurrection.
For a reflection on Lenten Fasting, visit here. (United States Conference of Catholic Bishops, usccb.org)