Tinkerer was one of the first super villains Spider-Man battled in the comics, but the original character is much older than Logan Marshall-Green.
However, these superhero movies are adaptations, so going with a younger version shouldn’t be an issue as long as Spider-Man: Homecoming stays faithful to the character.
However, a few week ago, it was reported that The Tinkerer would be a supporting villain in the movie.
It’s been reported for several months now (but not officially confirmed) that The Vulture is the main antagonist in Spider-Man: Homecoming, so it stands to reason that’s who Keaton will play.