I agree. I'd prefer that they stay teenagers myself.
I believe the last time Mike Judge actually did anything with Beavis and Butt-head that involved providing their voices was back in 2005, when there were those promos for the MTV music awards that year, and the infomercial with Billy Dee Williams promoting the first Beavis and Butt-head: The Mike Judge Collection DVD set. They were just a tad different from back in the day, but still acceptable nevertheless.
A thought that just dawned on me is that since the article didn't mention anything about them discussing videos, they probably won't be doing that anymore in this new version. For all we know, the episodes could just be full 30-minute episodes as opposed to the 10-15 minute shorts from back in the day.