Abuse of children, sexually or otherwise, usually has no statute of limitaitons here in the U.S. However, it's up to each State since most of those types of crimes aren't prosecuted under Federal Law.
When read in their entirety, the accusations seem to have alot of holes in them. In one case, the woman maintained, by her own admission, a relationship with Cosby for several years after the alleged "rape". I'm afraid it's one of those "she said, he said" things that'll not easily be resolved. I'm also concerned that more and more women seemingly come out of the woodwork... which can infer guilt on his part or "15 minutes of fame" the accusers part... Why 30 or 40 years after the supposed event?