import-module activedirectory 
$domain = "your.domain.name" 
$DaysInactive = 90 
$time = (Get-Date).Adddays(-($DaysInactive))
 
Get-ADUser -Filter {LastLogonTimeStamp -lt $time -and enabled -eq $false} -Properties LastLogonTimeStamp |
 
select-object Name,@{Name="Stamp"; Expression={[DateTime]::FromFileTime($_.lastLogonTimestamp)}} | export-csv OLD_User.csv -notypeinformation