Q: At what age should we start thinking about wedding?
A: Thinking about marriage is not about age but about desire. Because one of its main objectives is to guard chastity, it is obligatory if you fear you will commit a sinful sexual act, preferred when you are experiencing strong sensual desires, and merely permissible if you are not. If you use those feeling as your guideline and not age, all will be well by the leave of Allah. Allah knows best.
Source: Sharh al-Muntaha