The correct way to establish the compiler environment is to use the "source" command as follows:
source /opt/intel/bin/ifortvars.sh intel64
Please see the documentation and "Getting Started" topic for more details.
As for old compilers, see https://software.intel.com/en-us/articles/older-version-installation/ Typically for older versions, only the last update is available. We strongly recommend using the current version.