I wanted to go to the Steve Lacy concert but its 18+ and im underage, could i get in if i go with someone 18+?

You can go with your guardian. If you are 17 and have an 18 year old friend you will not get in.

Seems like you should just call the venue. That's what I did when I had a question about the Royal Blood concert last week and it was much easier faster way to get my answer.

Yes if you accompanied by an adult

No you also must be 18