Microsoft has announced that it will be dropping support for the older versions of some of the operating systems for Skype. The applications has evolved to support a lot of new features over the years and understandably some of these platforms can no longer support them. That, or Microsoft just doesn't want the hassle of providing support for so many platforms out there, which is also understandable to an extent. The first platform to get the axe is Microsoft's own Windows Phone. Skype will only support Windows 10 Mobile and will drop support for Windows Phone 8.1 and 8 starting...
Source: http://www.gsmarena.com/skype_drops_support_for_older_versions_of_windows_phone_android_and_os_x-news-19528.php