How to Build Your Kid's Credit Score

I purchased my first home when I was 22. I didn’t have enough cash to pay the entire down payment, but my lender didn’t mind because my credit score was already high enough to convince them I could handle more debt. This was made possible due to my parents’ insistence that I start using a credit card as soon as I turned 18. I didn’t know how useful building credit would be at the time, but I certainly understand now. This begs the question: At what age can someone begin building credit? And what are some ways to do it?