He meets all of the other requirements in the T&Cs for the Student pricing, except he is not 13. Can I sign up and provide his student credentials to obtain the discount?
Student discount is available to qualifying students/teachers as detailed here:
Am I eligible?
To qualify for a student discount, you must be at least 13 years of age and enrolled in one of the following:
• University or college — accredited public or private university or college (including community, junior, or vocational college) that grants degrees requiring not less than the equivalent of two years of full-time study*
• Primary or secondary school — accredited public or private primary or secondary school providing full-time instruction*
• Homeschool — defined by state homeschooling regulations
Unfortunately he'll need to wait a bit longer before he qualifies for the discount and is eligible to use the services.