$cutoff = (Get-Date) - (New-TimeSpan -Days 30)
$before = (Get-ChildItem $env:temp | Measure-Object Length -Sum).Sum

 

Get-ChildItem $env:temp |                           
 Where-Object { $_.Length -ne $null } |            
 Where-Object { $_.LastWriteTime -lt $cutoff } |
 Remove-Item -Force -ErrorAction SilentlyContinue -Recurse -WhatIf
$after = (Get-ChildItem $env:temp | Measure-Object Length -Sum).Sum
$freed = $before - $after
'Cleanup freed {0:0.0} MB.' -f ($freed/1MB)