I pay my mom’s medical expenses. She’s 83 years old and I’m 60. What percentage of adjusted gross income (AGI) to I apply for itemized deductions?

In 2013, the AGI floor for someone under age 65 is 10% of AGI. The 7.5% floor applies to those 65 or older. Since it is you, and not your mom, who is taking the deduction, you must use the 10%-of-AGI floor.