[CmdletBinding(SupportsShouldProcess=$True)]
Param(
   [int]$CutoffDays = 150
)

$cutoffDate = (Get-Date).AddDays(-$CutoffDays)

# get path to cached NuGet packages ("%USERPROFILE$\.nuget\packages")
$nugetCachePath = Join-Path "$([System.Environment]::GetFolderPath([System.Environment+SpecialFolder]::UserProfile))" ".nuget\packages"

# get all package versions
$packages = gci -Path $nugetCachePath | gci

# get only those folders which weren't accessed since $cutoffDate, and also get their lengths
$oldPackages = $packages |
  ? { $_.LastAccessTimeUtc -le $cutoffDate } | 
  Sort-Object -Property LastAccessTime | 
  select Fullname,LastAccessTime,@{Name="Length";Expression={ (gci $_.Fullname -Recurse -Force | Measure-Object -Property Length -Sum).Sum }}

# delete those folder
$oldPackages | select -ExpandProperty Fullname | Remove-Item -Recurse

# output freed bytes
"{0:n2} Mb freed" -f (($oldPackages | Measure-Object -Property Length -Sum).Sum / 1Mb)