You’re getting this because you’re running PHP 5.2 on your server. The plugin requires PHP 5.3. If it did not do this check, you would get an error when it tried to use a PHP 5.3 feature.
I won’t recommend a plugin as that would be offtopic and result in the question being closed ( hint: edit that out of your question ).
The fix, is to upgrade to PHP 5.3, or even better, PHP 5.4. PHP 5.3 is already nearing end of life, and PHP 5.2 is significantly slower than 5.3, insecure, and has bugs. 5.5 is due out soon.
For reference PHP 5.2.4, the minimum needed version, was released in February 2007, at least 6 years ago.
Contact your host or server administrator and demand an update. It is long overdue