Taking friends out to dinner or giving them presents is meaningful in part because it signifies how we feel toward them right now. A graduation ceremony is meaningful because it occurs at a moment when people have completed an important stage in their education. One reason for the current question about what age is right for Confirmation is that people cannot all agree about what exactly the sacrament should point to in the lives of those being confirmed.
It is easier to see what other sacraments are celebrating, however. For example, through the Baptism ceremony, some people are entering the Christian community while others are supporting and welcoming them into community. In Matrimony and Ordination ceremonies, people are likewise undergoing important changes in their relationships with others through the very process of the ceremony.