I'd say 80% of this is traceable to having a comfortable amount of money his entire life and decent, non-abusive parents. A lot of anxiety and mental illness most people experience is traceable to trauma due to scarcity or trauma due to family. Ditto sleep disorders and reactability.

It doesn't explain everything, of course. No allergies is just a lucky die roll (and may not be true forever; allergies sometimes develop over time, or appear because you finally tried something new). And plenty of mental illnesses can still develop no matter who you are.