I realise that a) I'm not a lady and b) I'm persona non grata at the moment and therefore may not be welcome here, so if you want me to feck off, say so; but a few thoughts:
Age difference isn't in and of itself a problem - my Dad, rest his soul, was 18 years older than my Mum; they met when she was 25 and he was 43. No-one batted so much as an eyelid (so I'm told - I came along a couple of years later).
Personally I think it's more a case of the relative ages. Sure, at 16, the age of consent has been reached; but a 16 year old is still technically, at least in the eyes of the law, a child. For someone much older than, say, 20, to be involved with a 16 year old would give me considerable pause. That said, I don't think there's a definitive answer to the age difference issue. The whole age thing in the UK needs sorting - for example the law says that people aged 16 can marry and have sex, which presumably means that society thinks they're ready to bring up children and make decisions for their child's future; but those same 16 year olds aren't deemed to know their own minds sufficiently to be allowed to vote or buy their wedding guests a celebratory glass of Champagne.
Ann, from a purely legal viewpoint (and I'm not a lawyer) I don't think what happened to you could be classed as sexual abuse if a) you were over 16 when the relationship became sexual and b) you consented. From a moral viewpoint, it's a totally different story - if nothing else your trust was abused, as someone three times your age should not have taken advantage of a vulnerable young person for what was presumably his own gratification.