Each one has their own specific requirements, since there are general guidlines in Canon Law. Usually one must be fully initiated and a proper role model. Some dioceses regulate an age, such as18, but others do not.
Some pastors regulate for the parish too.
Mass. The ordinary minister of the distribution of the Eucharist is the priest who presides at the celebration. However, when there are large numbers of people receiving Communion, various assisting ministers are employed. When present, the deacon distributes the cup and may also distribute the host. Thus, extraordinary eucharistic ministers may be appointed whenever the lack of ordained clergy would unduly lengthen a service or whenever the spiritual needs of the infirm in homes or hospitals require it.