Before asking someone to be a sponsor for baptism or confirmation, know that a sponsor is to help the baptized or confirmed lead a Christian life in harmony with baptism and fulfill faithfully the obligations connected to it.
According to Church Law, a sponsor must:
Be designated by the candidate, or in the case of infant baptism, by the candidate's parents.
Be at least 16 years of age (the pastor may make an exception for a just cause).
Be Catholic, and have received the Sacraments of Initiation (Baptism, Eucharist, and Confirmation).
Lead a life in harmony with the faith and the role to be undertaken.
Be living in a valid union (a marriage recognized or blessed by the Catholic Church).
Other important points:
A candidate's parents may not serve as sponsor.
Only one sponsor (male or female) is required, but two sponsors, one of each, are permitted for baptism. You may not designate two godparents of the same sex.
A baptized non-Catholic Christian cannot be a Catholic sponsor, but may assist as a Christian witness. (A baptized Catholic who does not meet all eligibility requirements may not serve as a Christian witness.)
A person's baptismal sponsor may also take this role at Confirmation, provided that he/she still meets the criteria above.