Lenten Fast and Abstinence rules can be seen on the USCCB page here.
Ash Wednesday and Good Friday are obligatory days of fasting and abstinence for Catholics. In addition, Fridays during Lent are obligatory days of abstinence.
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.
Members of the Eastern Catholic Churches are to observe the particular law of their own sui iuris Church.
During Lent, Roman Catholics observe abstinence and fasting:
1) Abstinence on all Fridays of Lent, as well as on Ash Wednesday and Good Friday.
No meat (except seafood) may be eaten on days of abstinence. This applies to Roman Catholics 14 years and older. Pregnant and nursing mothers are exempt, as are all who are ill.
2) Fasting on Ash Wednesday and Good Friday.
Fasting means having only one full meal to maintain one’s strength. Two smaller, meatless (except seafood) and penitential meals are permitted according to one’s needs, but they should not together equal the one full meal. Eating solid foods between meals is not permitted. Liquids are allowed to be taken between meals.
Roman Catholics from age 18 through age 59 are bound to fast. Again, pregnant and nursing mothers are exempt, as are those who are ill and those engaged in heavy manual labor.
These are the communal minimal requirements that we are to observe. Catholics are free to abstain and fast on other days of Lent as individual expressions of penitence. Sundays, as days that mark the Resurrection of the Lord, are traditionally not days of fasting and abstinence, although individual Catholics are free to fast and abstain on Sundays if they so choose.