Age for Confirmation

I have friends who are preparing to be confirmed at 15 and other friends who say they were confirmed at 7. Why the disparity?

The normal sequence of the sacraments of Initiation for the Catholic Church is: Baptism, Confirmation, Eucharist. Universal Church law and the Catechism of the Catholic Church still presume confirmation prior to First Eucharist. A little over 100 years ago the pope, to encourage people to receive communion more often, lowered the age, at the time , of First Eucharist to the “age of reason” determined to be 7. The age for confirmation at the time was unchanged. This led to the common custom of Confirmation after First Eucharist. Pope Benedict XVI pointed out that there are no doctrinal or sacramental reasons for a delay for Confirmation, only pastoral ones; and that the custom should be re-examined. Most of the bishops I have asked said they keep Confirmation later to force the children to stay in a religious education class longer, certainly not a theological argument. Some bishops have restored Confirmation to its theological location before first communion, others have not. The USCCB has designated the ages between 7 and 18 for Confirmation in the Latin Rite.
Your friend already confirmed at 7 could have several reasons. If a child is baptized or received into the Church after their 7^th birthday they are to be confirmed, it is not optional to delay such. In addition, if a child is in danger of death the priest is to confirm them, regardless of their age. Also, those who are baptized in one of the many Eastern branches of the church are confirmed after baptism as an infant. This leaves us with some younger children already confirmed and others having to wait until a later age.
Thus, there is no theological or sacramental reason for someone being confirmed at an older age, simply the personal preference of the local bishop.