Skin will shrink to some extent at any age, but the older you are the less it shrinks and the more slowly it shrinks.
Past a certain point stretched skin stays stretched, at which point only surgery can remove it. This should be done only after extensive consultation with a plastic/reconstructive surgeon, who will be able to examine the person in question thoroughly before making judgements about their individual case.
I’ve also heard that the more weight you lose, the more likely you’ll need surgery. I’ll second Broomstick’s recommendation of a consultation with a surgeon.
I just saw a program on this. For some people (like Oprah) the skin shrinks and all is well. For others, the skin will always be stretched out. There is a procedure called the “body lift” where they cut a section out of your middle and then sew the skin back together. They do the same on arms and legs. It is very high-risk surgery because of the chance of infection. It is very painful and very expensive. http://www.infoplasticsurgery.com/bodyphotos.html shows pictures and gives information on exactly what’s going on.
I suggest your friend speak to a surgeon and get the scoop from someone who knows the details. This makes lipo look like getting a manicure. Good luck to him!