Using old versions of GZDoom is not forbidden - in fact, an entire repository (archive) was made available, more for historical interest but also as a development aid (i.e. bugtracking).
One thing people do not understand, however: Use of these builds is NOT sanctioned nor supported by the development team! Officially we will only offer support for the latest released version. If you have an old version of GZDoom and something breaks - you're SOL until you upgrade. As of this post (may or may not be updated in subsequent releases, but judging by this post's date you should be able to guess what I am getting at), that means no build except 4.5.0/3.87a is officially supported. Not even 3.2.4 is supported. 3.2.0 is not supported. 3.1.0 is not supported. 3.0.0 is not supported. 2.2.0 is not supported. 1.8.6 is not supported.
If you need a more up-to-date version of GZDoom that's still supported but offers the old renderer, please consider the ZDoom32 project.
I still see people going around purporting these old versions of GZDoom for general use - if you have issues with the newer versions of GZDoom, it does not hurt to file a bug report. We also have a troubleshooting forum that you can use if you have less bug-related but more technical-related problems.
I will make this very clear: Using old versions of GZDoom, QZDoom, or ZDoom is highly discouraged!