I've been looking around and couldn't find an archive for previous versions of Android where you can checkout how GUI was done back then.
I'm developing an application and want to make its UI consistent with the platform version it's running into.
Any help would be much appreciated.
Do correct me if I'm mistaken but prior to Material Design (API 21+) there wasn't any thoroughly documented and specified guidelines for Android apps.
Your best bet is to use some sort of internet archive browser services, such as The Wayback Machine, and explore Android's own design page - d.android.com/design.
As a starting point, here's said page captured on January 1st, 2014. You could still see informations about Holo there. I imagine you could go even further to the past to find more.