Issue in looping through drives and servers

Question

I'm trying to write a script which scan through all the drives and find old files with specific extension on the list of servers which I pass in servers.txt. Please find below the errors and the script which I executed. Can anyone suggest 1) why it is checking
in my local desktop drive rather than server listed in servers.txt.2) How to pass a value to a variable :$diskname="\\$strComputer$\$disk$"
Error Message 
starting
Cannot find an overload for "op_Subtraction" and the argument count: "2".
At C:\Documents\oldfiles_new.ps1:29 char:25
+    $time = ((Get-Date) - <<<<  $file.CreationTime).Days 
    + CategoryInfo          : NotSpecified: (:) [], MethodException
    + FullyQualifiedErrorId : MethodCountCouldNotFindBest
\\.$\\\local_host\root\cimv2:Win32_LogicalDisk.DeviceID="D:"$
Compiling list, this could take a while.
Get-ChildItem : Illegal characters in path.
At C:\Documents\oldfiles_new.ps1:25 char:23
+ $files = get-childitem <<<<  $diskname -Include *.trn,*.bak -recurse  
    + CategoryInfo          : InvalidArgument: (\\.$\\\ACWIN-MG....DeviceID="D:"$:String) [Get-ChildItem], ArgumentException
    + FullyQualifiedErrorId : ItemExistsArgumentError,Microsoft.PowerShell.Commands.GetChildItemCommand
Script which I executed:
function oldfiles {
Param( 
    [alias("f")] 
    $outfile, 
    [alias("a")] 
    $maxage, 
    [alias("d")] 
    [string] $strComputer) 
#If a parameter was not specified, set a defualt 
if (!($strComputer)) {$strComputer = "."} 
if (!($outfile)) {$outfile = "C:\Documents\oldfiles.csv"} 
if (!($maxage)) {$maxage = 10} 
#param( [string] $strComputer) 
    # Get the Disks for this computer
    $colDisks = get-wmiobject Win32_LogicalDisk -computername $strComputer -Filter "DriveType = 3"
foreach ($disk in $colDisks) {
$diskname="\\$strComputer$\$disk$"
$diskname
Write-host "Compiling list, this could take a while." 
$files = get-childitem $diskname -Include *.trn,*.bak -recurse  
"File Name `t Age in Days " | out-file $outfile 
write-host "starting" 
foreach ($file in $files) { 
   $time = ((Get-Date) - $file.CreationTime).Days 
#$totalSize = {($file).Length -gt 5kb }
   if ($time -gt $maxage -and $file.PSiSContainer -ne $True) {"$($file.FullName) `t $time `t" | out-file -Append $outfile}  
foreach ($computer in cat C:\Documents\servers.txt) {oldfiles $strcomputer}
Any help would be appreciated
Thanks

Answer 1

This will get you close but it will take forever to run.
function oldfiles{
Param(
$outfile='C:\Documents\oldfiles.csv',
$maxage=10,
[string]$computer=$env:COMPUTERNAME
$date=[DateTime]::Today
$colDisks=get-wmiobject Win32_LogicalDisk -computername $computer -Filter 'DriveType = 3'
foreach ($disk in $colDisks){
$driveletter=$disk.DeviceID.Split(':')[0]
$diskname="\\$computer\$driveletter$"
Write-host 'Compiling list, this could take a while.'
$files = get-childitem $diskname -Include *.trn,*.bak -recurse
"File Name `t Age in Days " | out-file $outfile
write-host "starting"
foreach ($file in $files) {
$time = ($date- $file.CreationTime).Days
if ($time -gt $maxage){
"$($file.FullName) `t $time `t" | out-file -Append $outfile
foreach ($computer in (cat C:\Documents\servers.txt)){
oldfiles $computer
¯\_(ツ)_/¯