I adopted him a year ago.
He's a rescue, so no papers, but he's about 2.5 - 3 best guess.
He wasn't neutered until about a month before I got him.
I first encountered the behavior when someone with two Airdales (1 adult & 1 juvenile) brought his to the field where we were. His younger dog stood still and stared at my dog. He stared back for a minute, and then went nuts. Fortunately, there was a fence between them.
He saw that same dog a couple more times, and immediately got aggressive, and now any Airdale he sees causes a reaction.