Karen Allen was interviewed, and opined about Indiana Jones's relationship with a young Marion

There's much more to the interview:

Over the last few years that scene has gotten attention because when the two are discussing their past and Marion’s says, “I was a child.” And Indiana Jones says, “You knew what you were doing.” I’m curious what you think of that, because there are some sinister undertones there.

Yeah, I guess you could say that. I think I say I was 16. I don’t know. That’s always what I imagined is she was 16, he was 26. And he was her father’s student. And it’s left very mysterious.

It is.

So we don’t even know what it is. I mean, they could have kissed a few times, and she was just completely bowled over, and he could have just not wanted to get involved with someone so young. And maybe my father would have been furious at him. I mean, what’s great about it is we don’t know what the circumstances are. So she obviously cared deeply for him. He may have cared for her, too. But, in the end, decided it was a dangerous situation and he didn’t want to be involved. I mean, I guess, when something is as vague as that, you can color it any way you want to color it. I’ve tended to color it, sort of, that it was quite innocent. When she says, “It was wrong and you knew it.” I mean, I think maybe he led her on in some way. But when she says she was a child, I think she meant she was 16. Something like that.