Within the rate settings for each property there is an option to turn on / off the requirement to enter guest names and ages during the online booking process.
Turning on Name/Age Requirement

Navigate to Rates / Rules tab within property setup
Click on the Rate Settings button
Turn on require guest names
Turn on require guest ages
Note that per person rates must be turned on before you can require guest names and ages.
Example of Requiring Guest Names / Ages - Online Booking

Guests will be required to enter names and ages of each guest when booking online.
Example of Guest Names / Ages - Manual Bookings

Navigate to the Guests tab of the Guest Control Panel
Click the Add Guest button
Add the guest name and age
Example of Requiring Guest Names / Ages - Rental Agreement
When require guest names and / or ages is turned on, the merge tag for [GUEST_NAMES] will populate within the guest names and ages within the rental agreement.