types/FileInfo.Types.ps1xml

<?xml version="1.0" encoding="utf-8"?>
<Types>
    <Type>
        <Name>System.IO.FileInfo</Name>
        <Members>
            <ScriptProperty>
                <Name>Age</Name>
                <GetScriptBlock>
                    ((Get-Date) - ($this.CreationTime)).Days
                </GetScriptBlock>
            </ScriptProperty>
        </Members>
    </Type>
</Types>