Hi surya2020
Installing quickstart package will be the same as installing Joomla package, it's used for a new website. So when you said that it can't be installed in Joomla 3.x, I guess you're trying to install into an existing Joomla site, right? I'm afraid it will not work.
If you want to use T4 Page Builder in an existing site, you will need to download component + plugins of T4 page builder, not 'Quickstart' package.
Regards