Are we vulnerable to reverse discrimination claims because of our ‘early out’ program?

Q. Are there any specific rules defining “early out” retirement packages offered to employees? Our company is planning to offer early outs. Our criteria mandate that an employee must have worked for us for at least 15 years and be at least 50 years old. But we have employees who have worked as long as 28 years who fail to meet the 50-year-old criterion. Is this age discrimination in a reverse sort of way?