Things you are not entitled to know about your customers: anything else whatsoever.
Asking for people's age, gender, or whatever, is creepy and rude. Especially if you inconvenience the customer in the process.
And...
(a) You can comply with COPPA and similar laws by not collecting data on ANYBODY, which is what you should be doing anyhow. No sympathy.
(b) Let the customer decide what the customer wants, thank you very much.