You dont need an instructor, but it would not be a bad idea. Like oefdevilvet said it would help with confidence more than anything. Just go at it alone first to see what you think you need to work on. Just make sure you take safety as your 1st priority. Start with small features or jumps and pick a day when the snow is soft. Try to wear some protective gear. At minimum helmet wrist guard. maybe knee pads. wrist guard and knee pads are pretty common so you can borrow them if you don't have them. Try to go with some of your friends so they can give you some tips and watch over you.
If you are too scared to start going to park you can start with ground tricks. Like buttering, pretzel or little 180s or simply riding switch.
And your gear should be ok unless you have really stiff big mountain board.
Since you prob have beginner board, it should be flexible enough.
And 14 is not too late to compete if that is what you want to do.
And don't worry about judgemental people at the park. Its prob mostly in your head. They are just waiting for their turn. They have to look at you to make sure you are out of their way before they go. If they are really A-holes, take even more time to piss them off.
Join the weekend club. at minimum you will meet someone you can ride with. It's more fun to ride with friends and they may be able to teach you thing or two