I haven’t seen that many people who I could identify as coming in with their parents but I have seen people of all ages from 21 to 75 come in. I would imagine that it has happened before and will happened again. The big thing is just make sure however you come, you are comfortable with it. Also I will tell you you won’t be, and that is normal. The first time I came out I was a nervous wreck. I would recommend letting your parents drive you honestly because the limo is “free” but they do get a large cut of the party which can make negations a little more difficult.
What might work out better is if they got a room at the hotel. They would be able to come in separately if that is what you want and you would not be rushed. The rooms are not that expensive. The only suggestion I have is spend the extra money for a suite. If afterward you didn’t want to go back Las Vegas right away you could get a room for yourself also because after most parties you get a room certificate.