Post-sex vaginal tear with light bleeding. Could his penis be too wide?

Penis. Post coital bleeding may be significant, but if occurs only once, probably secondary to trauma. Use lots of lubrication. Unlikely it's too wide.
See your gyn. I have seen this possibility a number of times. However, post-coital bleeding should be evaluated by your gyn. Depending on your menopausal status and the source of the bleeding, this may have different medical implications.