Anyone know of a way to monitor for SNapshot age on a Hyper-V machine?

Yep, that’s it. Invoke-Command -computer <hyper-v name/ip>. Remember the powershell runs on the collector, which is why you need to run it remotely, unless the get-vm|get-vmsnapshot cmdlet has a remote option built in. 

I suggest a discovery script that would list out either the VMs or the snapshots (probably the VMs) and a batchscript collection script that lists out the age of the oldest snapshot on the VM (or the age of each snapshot if your discovery lists each snapshot individually).