Before we consider what Confirmation is, let us first look at what it is not:
Confirmation is not a graduation from catechesis. While confirmation-oriented catechesis is necessary prior to confirmation, general high school catechesis continues through the senior year. Not only that, but catechesis is really a life-long process, which is why St. Luke also has General Adult Education classes on a regular basis. In fact, some people are confirmed prior to their high school years. Catecheis, at an age-appropriate level, always challenges us to grow in our faith no matter what our sacrametnal status.
Confirmation is not primarily a rite of passage; it is not a way of moving into faith as an adult. Some would say that, in choosing confirmation, we make an adult decision. While this
can be a function of confirmation for some, it is not the primary function of confirmation. Some RCIA candidates are confirmed as young as age seven, and Chruch Tradition even allows for for infants to be confirmed.
Confirmation is, strictly speaking, not necessary if one want to get married in the Church. Confirmation is strongly recommended before marriage, or even shortly after, but it is not required.
Here is what confirmation is: Confirmation...
Both confirms baptism and strengthens baptismal grace (CCC 1289)
[Is] a more lively familiarity with the Holy Spirit [and] his gifts (CCC 1309)
Gives us a special strength of the Holy Spirit to spread and defend the faith...as true witnesses of Christ (CCC 1303)
[Is] a more intimate union with Christ (CCC1309)
Marks our total belonging to Christ (CCC 1296)
[Awakens] a sense of belonging to the Church of...Christ (CCC 1309)