What should I do concerning the past years during which a full year (hawl) has passed on my salaries, knowing that I did not pay zakat on my monthly salary due to my ignorance of the ruling, and is it permissible to pay more than a quarter of a tenth (2.5%) in zakat?

Zakat (definition) on salary becomes obligatory if it reaches the nisab (definition) and a full year (hawl) passes on it. The nisab is equivalent to the value of 85 grams of gold or 595 grams of silver. If you spend your salary and do not save an amount that reaches the nisab and on which a full year passes, then there is no zakat due on you. However, if you save an amount from it that reaches the nisab and a full year passes on it, then you must pay zakat for every past year. Zakat does not lapse with time; it must be paid immediately, whether the delay was due to ignorance or negligence. You must ascertain the amount of zakat due, and if you pay more, that is better.