The actor, Sam Neill, was in his mid 40s when Jurassic Park was filmed. So he wasn't quite 50 but still more than a little bit of age gap. Artistically I'd say it worked because I always thought he looked younger in the film (mid to late 30s) and Laura Dern looked older in the film (late 20s early 30s). Which kind of closes that age gap into something less creepy.