There is no age limit to qualify for EIC for someone who claims a qualifying child on their tax return, has earned income and does not exceed the earned income or AGI limits. Was your handicapped son totally and permanently disabled and did you claim him as a qualifying child? Did you have earned income (social security is not earned income) and was it and your AGI below the income limits? If you meet all the requirements, you should appeal the IRS's decision. Did they send you a letter and tell you what steps to take if you disagreed with them?
Here are the qualifications for getting EIC: https://www.irs.gov/publications/p596
