I say, and with God's success: The original ruling regarding the insane person; who is someone who reaches maturity while insane, is that there is no zakat (obligatory charity) on him. However, if he regains his sanity, zakat becomes due on him after one year from the time he regains his sanity, provided he possesses the nisab (minimum amount of wealth). As mentioned in Tabyin al-Haqaiq (1: 252/253), and God knows best.