Auto action - add user group to users under age 25

I need to add users who have entered a birthday in a date field, and who's birthday makes them younger than 25, to a certain user group - how would I do that ? How can I test against a date - 25 years ? And also, could I afterwards run this as a batch every day to automatically remove the group when they become older than 25 years ?

Was this possible at all ?

That's specifically what the Batch feature is for. Lets you run an auto action against a set of users. You'll need to use an Advanced Filter in your batch though as you'll need to use MySQL functions to check the date of whatever field you're using for birthdate.

You'd need 2 batches and 2 auto actions. 1 batch check if they're under the age of 25 and are missing that usergroup. The other checks if they're over the age of 25 and do have that usergroup. 1 auto action adds the usergroup and the other removes it. Now you'd schedule CRON to run the batch URLs using wget on whatever interval you like.

An alternative is you do this at time of login. So when they login it checks their age and adds/removes the usergroup as needed. That's a simpler approach if this is only needed to add or remove access for the user and won't be used for some sort of filtering/searching behavior.