My mom was given Gold for life last month. She's probably only flown 50,000 miles since she joined AAdvantage in 1994. Aside from a few bonuses, the rest were definitely from her Citicard.
Just so that the original poster doesn't go out and spend $1 million dollars in a day to get Gold, the number of miles you can earn as regular AAdvantage member using a Citicard is limited (citicards.com):
The maximum number of AAdvantage® miles you can earn with the Citi® Gold / AAdvantage® World MasterCard® is 60,000 AAdvantage® miles per calendar year, 100,000 AAdvantage® miles per calendar year with the Citi® Platinum Select® / AAdvantage® World MasterCard and 150,000 AAdvantage® miles per calendar year with the CitiBusiness® / AAdvantage® Card (purchases recorded on your Jan.-Dec. billing statements). AAdvantage Executive Platinum®, AAdvantage Platinum® and AAdvantage Gold® members are excluded from these limits.