Under the EGTRRA Act of 2001, employees who are eligible to make elective salary deferrals to defined contribution plans and who would be at least 50 years old by the end of the plan year can defer an additional amount to the plan as a "catch-up" contribution. The catch-up contribution starts once the plan participant reaches the maximum permitted statutory IRS annual deferral limit. As the employer you have the option as to whether or not you match an employee’s catch-up contributions.
Employers who match employee contributions also have the option to set a maximum for the annual amount that they will contribute for an employee. This is commonly referred to as the Plan Year Maximum.