Pull the starter off and spin the drive gear over by hand. If the teeth are chewed but intact, file any sharp burrs off and call it good, then have a friend slowly turn the engine over by hand and look for broken teeth on the flywheel. Same deal as the starter gear, if a few teeth in a row are missing, it should be replaced. If the teeth are beat up but intact, it's fine.
When I started driving my truck ran very quietly and stalled very easily. It was not uncommon for me to try and start the engine while it was still running because I thought it had died. My original starter and flywheel actually looked pretty good when I took them out.