When should I change my hairstyle?

I'm a 15 year old boy, and I wear my bangs down, and usually in a Beatles-esque style. I've been doing this since I was about 11 or 12, and it's been gradually in the same style, just getting shorter, its to the point now that when I get it cut, the bangs are down to the middle of my forehead. When I get older I want to start wearing my hair back, and the style I like is Chris Moltisanti from "The Sopranos". I think this might look good on me, because I look good with hair back (I haven't gotten it exactly right because I don't want to get my hair cut specifically to this style yet), I have a similar hair line, color, and I look a little like him except I have a round face, and not to brag or anything, but I think I have a perfect nose (his is big), I have the same bushy eyebrow shape as him, and I also have olive skin type and brown eyes like him, but that doesn't really pertain to this question. But when should I start this? I planned to do it in my 20's, but my sister is a cosmetologist and she said she thinks it looks like an old man's hair cut, I disagree, and I want to get some more opinions on this. I also have pretty thick hair, and she said the style might not look bad on me, but she just doesn't like it in general, she says when I change it I should have it like Neal Caffrey from "White Collar".