This article will help you how to enable google page speed in old os Centos 6. Cpnginx is using the latest google page speed module and it need GCC version 4.8 or higher . So you need to enable gcc latest version as follows,

# sudo rpm --import https://linux.web.cern.ch/linux/scientific6/docs/repository/cern/slc6X/i386/RPM-GPG-KEY-cern
# sudo wget -O /etc/yum.repos.d/slc6-devtoolset.repo https://linux.web.cern.ch/linux/scientific6/docs/repository/cern/devtoolset/slc6-devtoolset.repo
# sudo yum install devtoolset-2-gcc-c++ devtoolset-2-binutils

After installing the gcc, please set the PATH as follows in your shell,

# export PATH=/opt/rh/devtoolset-2/root/usr/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/opt/cpanel/composer/bin:/root/bin

Now you may go to WHM -> Cpnginx ->Settings and enable the google page speed module and compile it as follows,

# nginxctl build nginx

This will install and configure your cpnginx with latest google page speed module.