Brian, when I PM'd I mistakenly thought the guy was 19, hence my view that the ages were pretty much peer group, which now I find they very much weren't.
To put things into another context, I'm sure we'd all agree that most humans, given the chance, experiment sexually when they're young. We don't tend to wait until we're 94 before finding out how things work, so it would be entirely 'natural' for teenagers to experiment, whether that's boy-girl, boy-boy, or girl-girl. It's probably taken for granted (and I'm not debating whether it should be or not) that by the age of 19 or 20, a majority of young people will have experienced some sort of sexual encounter.
The thing is, I don't think any court is going to waste its own time considering the thousands of sexual encounters made during puberty as if they were criminal acts. Girls often initiate the encounters, sometimes with their much younger brothers, to find out how things work. These aren't serious relationships, they're more of the poke 'n' probe variety, along the lines of playing Dcotors and Nurses - and yes, even in my Mother's day, c.1920s, kids were taking off their kit and examining the various interesting bits!
However, to be more than twice the age of a CHILD, to be her or his teacher, and to have engaged - we may be being presumptuous, but it's more than likely - in sexual practices of some sort, is abusing a position of responsibility towards the child. It's, to put it plainly, taking advantage - regardless of whether the child is up for it or not. Wait until she or he is legally consensual, and then see how things go. A man of 34 can't excuse himself on the grounds of it being a bit of 'finding out', and should have had enough self-control to wait until the girl became, legally if no other way, a woman. Otherwise you may as well throw away all the well-meaning legislation about adults not abusing children for their own satisfaction. That they went on to marry happily is, as is said, irrelevant to what actually happened prior to the wedding. What if she'd become pregnant, and deeply UNhappy? What would the take on that be - oh, fooling around with kids is okay, as long as they're happy for some time afterwards?