If according to Technical Task, activity of customer account doesn't matter - means you need anyway to monitor age - I suggest you Create New table (add to DB) with fields whatever PrimaryKey, CustomerID ..., CreateAccountDate, ParentalSupervisionDate
.
Then Create a new Task and 2 new stored procedure (SP): ...Add...
and ...Check...
where
...Add...
SP will run on creation of account for person with age less than 18, and fill appropriate fields with dates when you need to act.
Ex. customer birthday is on ...2010. You fill field "CreateAccountDate" with ...2022 and field "ParentalSupervisionDate" with ...2028.
...Check...
SP will run every night checking appropriate dates (comparing with current date) and returning customer accounts that you should modify.
Create temp SP
that run once to fill in that New table with the data of already existing customers with age under 18 of course.
Then Add temp SP
and ...Check...
SP to that new task, run the task, and remove just temp SP from the task after it completes. First should Run temp SP
.
(DO NOT modify existing tables - very bad practice - in your case not needed)
At the end you will get one service that will run ...Add...
SP on account creation and a Task that will run every night ...Check...
SP that will return to second service (or whatever) a list of customers (customer accounts - better) that must be modified (usually are used DataSets).
And of course no need to delete anything - that's also a good way.