This film defies age. I don't know how many of my teenage guy friends still enjoy the Indiana Jones movies. My favorite is The Last Crusade, but this is a good one too.
That said. I don't understand why so many people let their children see this movie. I saw it at age fourteen and it was still intense. People get impaled through the head with spears. Riddled with blowdarts. Burned to death. Shot and have blood dribble out of their mouth. Melted. Have their heads explode. Get shredded by an airplane propeller and have their blood spray a window. Some of this is fairly fake-looking, but I don't think that mitigates the violence. The Indiana Jones films try to gross you out with disgusting violence. This film was originally going to be rated R. Does that surprise anyone? It didn't surprise me at all. The language used in this film is overall not that bad for a PG movie in the eighties, but it should still be noted that there are about eight uses of cursing in this film (including one s-word).
Also, Indiana Jones and his girlfriend have a very strongly implied tryst. The film shows them kissing on top of a bed in a fairly sensual scene and later shows her naked wrapped in the sheets so no nudity is visible there. Earlier in the film, the said girl-friend's bare back is visible as she changes and she wears a dress that isn't terribly modest.
That all said, I think a lot depends on your teens when deciding whether or not to let them see this film. However, I don't think I'd let most kids under the age of fourteen see this particular Indiana Jones movie. The PG-rating is deceptive parents. Don't be fooled by it into thinking that this is a family movie. This was nearly rated R, remember? Treat it at least like a PG-13 (and an edgy one at that).