Query on custom field

[qpurser]

Using 4.1.12

I need to get following:
We have a rule at our forum if a member doesn't attend a club meeting within a year he loses his full member status and becomes again just a registered user on the forum.

Therefore I created a custom private field where I put in the date this user attended his last meeting.
I would need a query to display all those members who's last meeting attended (custom field) is greater as 12 months.
Just a display would be good but copying them to another usergroup would be even better.

Any suggestions how to do this?
Thanks for any help
Michael