I agree with what has been said. Most 4 year olds, unless they've been consistently ridden with a well thought out training plan (not necessarily by a trainer, but by an experienced rider who has put considerable thought and effort into it) are still going to be quite green. There are the few 4 year olds that are of the 'born broke' temperament and would be potentially suitable for inexperienced riders, but they are few and far between, and this horse does not sound like one of them. On top of that he's been sitting for a year. I'd pass if you truly want something suitable for your BF.
“The horse is a mirror to your soul. Sometimes you might not like what you see. Sometimes you will.” - Buck Brannaman
"Nothing forced can ever be beautiful." - Xenophon