As my host offers me a choice of PHP versions from 5.2 to 7 (I currently use 5.6). I did play a little bit with Zenphoto as installed by Softaculous vs Zenphoto installed directly.
In a nutshell, Softaculous doesn't make a difference between a "warning" and a failure, and interprets both as a failure. So if you install Zenphoto manually, you'll get a *warning* that PHP 5.4 is better. If you install Zenphoto through Softaculous, it will *stop dead*, saying that your PHP version is incompatible. On the other hand, if I configure the server to use PHP 5.4 to 5.6, Softaculous will install Zenphoto perfectly.
What's the difference? Basically, with PHP 5.3, a couple of minor functions won't work. For instance, one of the upload methods (and I think the ELfinder) only work with PHP 5.4 and above. But the gallery itself – and the overwhelming majority of extensions – will work without problems.
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By the way, if you really look for an older version, you will find it at the download page here:
http://www.zenphoto.org/news/older-versions-archive
But as the current version works with PHP 5.3, why bother with an older one? Unless you want to add bugs?