Immediate friction or further up the journey?

Background

Our booking journey WILL require getting the exact age of any children added to the booking due to tax reasons. We are doing that by providing dropdowns to select the ages of these children.

We don’t have the data to estimate what a good default age is. Therefore if we was to have a default age it would be set at ‘0’ or ‘<1’. We are also testing the initial state of the dropdown as ‘-‘ where the user has to select an age before continuing with journey.

Problem

A - If the dropdown is default is ‘0’ or ‘<1’ Could the user ‘skip’ the age selection and complete their booking with incorrect child ages? This affects the price and could frustrate users further down the journey.

B - if the dropdown is ‘-‘ Does this create unnecessary interaction cost? Especially if the alternative state could be more accurate

Challenge

Would you prefer A or B?

Is there any findings over the impact of immediate friction against user created issues further down the journey (due to lack of error prevention). Also considering the peak end rule and error prevention which could mean option B is preferred.