Capacity to buy and sell is regulated by the general law concerning capacity to contract and to transfer and acquire property:
Provided that where necessaries are sold and delivered to a person who, by reason of mental incapacity or drunkenness, is incompetent to contract, the person must pay a reasonable price therefor.
Necessaries in this section mean goods suitable to the condition in life of such person, and to the person's actual requirements at the time of the sale and delivery.