Domain name ownership disputes

It won't be long before the next tech entrepreneur has a tech idea and finds the .com domain name for their idea but isn't old enough to register it so asks a relative or parents etc to register it for them until they are old enough to register it themselves?what happens if that said.com is a peach worth 6 figures or even 7 figures and was bought with relatives visa card etc who owns the domain name? and what if the legal owner doesn't want to hand the domain name over to the person then old enough to register it in their own name Who thought of the domain name originally and what proof and or rights would the person who thought of the domain name have?