Question: I spend about $20-30 a week on my debit card, with periodic $200-300 purchases every few months. I've thought about getting a credit card the moment I turn 18 and using it to buy everything, then immediately paying it off. Assuming I only use it to buy things I can afford (which I trust myself to do), essentially treating it as a debit card, is this a good idea? Or should I wait until I'm a bit older? 

Assume that I will only spend money I have in my bank account at the time I spend it and that I will keep track of how much I spent and never spend more than I have.

Joe Taxpayer recommended I post an update: I ended up getting a card, and from my perspective the only thing that's changed is that it takes things ~24 hours to show up on my statement and I don't have to enter a PIN when I checkout. Should I add this to the question? I know on other SE sites people generally don't like updates in the questions

Answer: 
The length of time you have established credit does improve your credit score in the long run.

As long as you can avoid paying interest, you might see if you can get a card with cash back rewards. I have one from Citi that sends me a $50 check every so often when I have enough rewards built up.
No, don't open a credit card. Get used to paying cash for everything from the beginning. The best situation you can be in is not to have any credit. When it comes time to buy a house, put down %30 percent and your 0 credit score won't matter.

This will keep you within your means, and, with governments gathering more and more data, help preserve your anonimity.