If you need to test whether some information resembles a valid date format, here is a test function:
function Test-Date { param ( [Parameter(Mandatory=$true] $Date ) (($Date -as [DateTime]) -ne $null) }
It uses the -as operator to try and convert the input to a DateTime format. If this fails, the result is $null, so the function checks for this and returns $true or $false. Note that the -as operator uses your local DateTime format.