When Buffett was starting his career he offered himself to work for free for Benjamin Graham, the pope of value investing and writer of Intelligent Investor, the bible of value investing.
Why would someone work for free? Because the experience and knowledge that you can get in this job is worth much more than money.
If you are young and in love with some activity, be open to work for free for someone that can inspire you in a positive way.
This video shows Warren himself explaining how his experience working with Graham has changed his life: