You will need to create a new system level role to do this. It will need at least the "Create users" (moodle/user:create) capability set to Allow, and those using this role will need to be able to view the Site admin menus to get to the options to add users. This is controlled by the capability "View the site administration tree (but not all the pages in it)" moodle/site:configview.
Take a look at the Manager role permissions settings for more information and in case you need to add more abilities to the role.
As I am sure you know, Moodle 2.9 is very out of date and not secure to use anymore. You should definitely upgrade.