First off this is a truly huge question that your asking, and I don't think it can be answered in any meaningful way without an essay being written.
Secondly, I'm a mathematician and this is a pure psychology/sociology question, being that my mind works on logic, guess how happy I am about this ?
So to recap the question. we have a 24 year old 'innocent' who has been thrust into a society he has no knowledge of, or any idea of how to interact with the average ( hate that word ) person. In effect what we have is a toddler rather than a man, so from my point of view that's where we start. Please also bear in mind I'm uniquely unsuited to child rearing.
So I suppose a general starting point would be Maslow's Hierarchy of Needs - http://en.wikipedia.org/wiki/Maslow's_hierarchy_of_needs
Physiological Needs
Ok, these are pretty straight forward and to the most part they have already been met.Breathing, Food, Water, Sleep, Homoeostasis, Excretion.
He knows how to breath, eat and drink. With those being met, homoeostasis and excretion are also met. Sleep will also have been met. BUT they have not been met in the context of our society. I'm making all sorts of assumptions here and I hate doing that, but saying that he will be more used to a hunter/gatherer society rather than the economy society we have. Therefore here's where we start.
Food - On the island I'm going to assume that he gathered his own food from the wild, prepared and ate it. Obviously this isn't going to work in the city, and his physiology won't be adapted to survive the processed food that as a majority we eat. So we need to slowly start introducing him to foods that are commonly available in the city.
Water - Again, on the island he's going to have been taking the water from nature, and again we treat all of our water with Chlorine and Fluoride for the first couple of days of drinking our water, he's going to be sick as a dog !
Sleep - Well this is the biggest of the needs that have to be met. In order for him to sleep implies the need for a dwelling of some sort. Being that he will need shelter and we can guarantee that he'll have no knowledge of things like indoor plumbing, gas, electricity and so on, he's going to need a mentor in order to protect himself from harm. That's where we come in, we're going to have to live with him. Now another question is raised do we bring him into an existing situation i.e. our home, or do we start afresh ?
That's all I've got for now, I may take another swing at it a bit later on, but right now I'm off to relax by baking cheese scones until I've nowhere left to hide them !!
But major major thanks for this question !