Can you attend court for a speeding ticket with someone other than your parent if your under 18?

Yes, a legal guardian can attend if one has been appointed.

If not - parent!

Four days of questions about this one ticket.  Pay the ticket and move on!  You are wasting time and energy with various theories about getting the ticket dismissed. It won't be dismissed.

IF you are required to have ANYONE with you, they must be your LEGAL guardian, and the court WILL demand proof of guardianship if that person doesn't seem to be your parent.

Without knowing WHERE, we can't determine if your parent/legal guardian is required to attend.

Note: It is IMPOSSIBLE to hide it from your parents.

you need to ask a lawyer about it

Your "friend" is NOT your "guardian".  

When fighting a ticket, you rarely win.

Your parents WILL find this out because it is very likely that you will also get a letter from the state needing  you to prove that you have auto insurance too.  They will need to have their insurance company send in that proof for the state.  

A friend isn't your "parent or guardian," though a judge might laugh out loud when they ask you who that person is and you say, "This is my 'guardian'," putting air quotes around "guardian," as you do.

If you appear with a guardian, that guardian must show proof of guardianship, i.e., a court order or a transference of guardianship signed by your parents and notarized.

Yeah you can go with your mate but they can't represent or talk for you.