All just my opinion only as I'm not sure how the process would work, offences etc... but I'd say initially it was, at least, some kind of sexual assault.
As for rape, I guess it would depend on whether, once awareness had kicked in, consent was not given (ie said or tried to stop etc...) or if consent was not able to be given.
I think the actual circumstances would very much come into play if anything ever got to court and there would be a lot of talk about motive for the late reporting, why now etc...
I always tend to look at how good a possible defence may be to try and guage that, however true or not, an honest think about what could come up in court eg any kind of relationship between the parties or others connected since ie could it be insinuated a grudge has led to a false report etc...
It's not to say looking into things couldn't be cathartic though, making a report, despite the outcome, or at least taking advice could help in feeling something is being done. This could be both police and legal.
As for taking any action, for me, it would depend on the effect it was having on the person or possibly other people, whether he is a potential dangers to others etc...
I think some kind of talking therapy with a trained counsellor would be good prior to taking any action.