You can only be a deputy for a person who lacks capacity if you are over the age of 18.
Ideally, the deputyship application should be made by someone who knows the person who has lost mental capacity well, understands their wishes and can involve them as much as possible in making decisions — for example, a family member or close friend.
In any event, before deciding to make an order, the Court will look at the suitability of the proposed deputy.