Is zakat obligatory on money deposited by a father for his son in the bank, which the son was unable to access for seven years, and then withdrew? And if it is obligatory, how are the past years calculated, and what should one do if they spent the money unaware of the obligation of zakat?

Zakat is obligatory on wealth if it reaches the nisab (minimum threshold) and a hawl (full lunar year) passes over it, even if you are unable to withdraw it from the bank. You must pay zakat for the past seven years, calculating the amount due for each year. The nisab for banknotes is approximately equivalent to 85 grams of gold, and the obligatory zakat amount is a quarter of a tenth (2.5%). If the money is in an interest-based bank, zakat is due only on the principal amount, while the usurious interest must be disposed of by spending it on public welfare. It is forbidden to deposit money in an interest-based bank except in cases of extreme necessity, and then only in a current account. Zakat is a debt on one's conscience even if the money is spent, and it must be paid as soon as one is able.