I'm wondering how I can make myself look older because I've been told that I look to be anywhere from 11 - 14 and I hate it because no one is gonna want to date someone who looks that young when I'm really 18 almost 19. Any tips would help me out a lot :)
You do have a face of a 15-year old. 11 is waaaay too low - people exaggerate.
Anyways, you need a shorter haircut + you have chubby cheeks (this is something you can't change, it is what it is - one of my friends has a chubbier head, while her body is normal - she doesn't look younger because of this).
Anyway... that haircut is doing you no favors. Find a more mature alternative (ask your hairstylist).
Get a shorter hair cut/style and dress more maturely. You can also workout/build muscle mass which will make you look a bit bigger/more masculine. Besides that, there isn't too much you can do to change how old you look.
I don't see how wearing a suit and tie on a daily basis will help anything, unless of course you have a job that requires that, otherwise you're just wasting your money.
From your pic I would say get a hair cut, shorter hair always looks better, and as far as your wardrobe goes, as long as you stay away from clothing that makes you look like a little kid you should be good, so if you're going out in public no gamer shirts, band t shirts, or or anything a 10 yr old would think is cool.
You could go out buy yourself a gym membership and like most people never use it. So next best thing find clothes that fit you.
Looking young isn't bad at all, I am in my 30s, married, and people still ask me what I am going to major in college, been there done that.
draw a mouthstache under your nose that's all you can do for now