You can do what you like with your money, but rest assured, most people will see you as a spoiled brat in a sports car. Not saying its right or wrong, just saying that its going to be most people's reaction.
If I were still 17, I'd want a Z, but I can honestly tell you that driving an old pos Jeep XJ beater I earned and payed for by working in a bagel shop was one of my favorite cars. Sure my parents could have bought me a new car, but I'm honestly glad they didn't. Kudos if you've somehow accumulated this money on your own. If mom and dad are the ones paying for it though, sounds like they're trying to make up for something
I've just seen too many 17 year olds racing and wrecking cars in my area to not be a bit skeptical. The statistics don't lie and most drivers aren't as skilled & exceptional as they think they are. At 17, you have 2-3 years of on-road driving experience tops. With one of your reasons for switching being the extra 20hp, it tells us that you're a bit naïve. Even starting this very topic makes you naïve.
If you're grownz up and want the Z, you buy the Z. You don't need our opinion on the Z being a good car and there are certainly plenty of threads on the pros and cons to ownership.