My English teacher took some points off on a recent paper of mine based on improper comma usage, so I'm coming here for clarification. Here are the examples. The [x]'s indicate where the commas were deemed missing and I was marked down accordingly.
When I was younger[x] I skipped the superhero phase, and never really thought twice about it.
At this point[x] the character becomes ridiculous as he becomes a God.
I was under the impression that commas are generally used to indicate pauses in speaking, connect independent clauses, delimit lists, or signal appositives. For example, many authors and speakers may use commas more frequently than others to indicate many pauses in speaking, whereas others prefer a more rushed manner of speaking (Had I been in a more pensive mood, I may have included the commas, but my manner of thinking at the time felt the chosen method more accurately represented what I was attempting to depict.)
Is one wrong and the other not? Is my teacher correct? Are there set-in-stone comma rules that are to be consistently followed in order to be proper? If so, are only creative writers and authors allowed to break those rules?
Thanks for reading.