How to find Disks that are not attached/used more than xx days?

Hey !
First of all i am so gradeful for your Detalied answers!!
i have been out for a few days and my task was changed to :

1. get the vms in deallocated state for more than x days ,
2. if those VMs have a disk that is greater than 50GB size , tag the VMs and the disks
3. delete the tagged resources.

but anyway you answer to find those disks will help me now.
i will give it a try and will let you know if it worked.
** sharing with you my code for this one :)

$ids = New-Object System.Collections.ArrayList
$mergedTags = @{"Candidate"="Delete Me"}
$vms =  (Get-AzVM -Status)
    foreach ($vm in $vms ) {
       $getStatuses = Get-AzVM -ResourceGroupName $vm.ResourceGroupName -Name $vm.Name -Status  
       $getTodaysDate = Get-Date
       $ts = New-TimeSpan  -Start (($getStatuses.Statuses).Time).DateTime -End $getTodaysDate  
           [bool]$flag = 0
           if (($vm.PowerState -eq "VM deallocated") -AND ($ts.Days -gt 30)) {
           $ids.Add($vm.Id)
                foreach ($disk in $getStatuses.Disks.Name) {
                    $diskSize = Get-AzDisk -ResourceGroupName $vm.ResourceGroupName -Name $disk
                    if ($diskSize.DiskSizeGB -gt 50) {
                        $flag = 1
                        $ids.Add($diskSize.Id)
                        if ($flag = 1) {
                            Update-AzTag -ResourceId $vm.Id -Tag $mergedTags -Operation Merge
                            Update-AzTag -ResourceId $diskSize.Id -Tag $mergedTags -Operation Merge
                        }
                    }
                }
            }
        }
    }