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: 
Yes, as long as you are responsible with the payments and treat it as a cash substitute, and not a loan. I waited until I was 21 to apply for my first credit card, which gave me a later start to my credit history.

That led to an embarrassing credit rejection when I went to buy some furniture after I graduated college. You'd think $700 split into three interest-free payments wouldn't be too big of a risk, but I was rejected since my credit history was only 4 months long, even though I had zero late payments. 

So I ended up paying cash for the furniture instead, but it was still a horrible feeling when the sales rep came back to me and quietly told me my credit application had been denied.
> 
> 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?
> 
> 
> 

This is definitely a good idea.

From my own experience, before I got my first credit card through my local bank (age 18), I tired to apply for a card that has cash back rewards and was rejected because I didn't have any credit history. After I had the card from my bank for 6 months, I applied for [this Capital One](http://www.capitalone.com/credit-cards/quicksilver/) card that I've had ever since.