It doesn't matter how old he was. He admitted he had the debt, reached a settlement agreement, and then defaulted on that. It's all right here in black and white....
http://articles.latimes.com/2012/mar/23/nation/la-na-nn-george-zimmerman-20120323
Zimmerman married Shellie Nicole Dean, a licensed cosmetologist, in late 2007.
The next year, he resurfaced in court documents as a credit-card company pursued him. Capital One accused Zimmerman of failing to pay more than $1,000. He settled with the company for $2,135.82, records show, to cover his debts with interest, as well as attorney and court costs. The credit card company soon reported that Zimmerman wasn't making the agreed payments. Zimmerman's employer at the time, CarMax, agreed to garnish his wages. That arrangement was canceled in late 2008 because Zimmerman was no longer working there.