Paying back child support on a 35 year old

(georgia)

In 1975 a judge awarded my ex-wife $250/month in child support. but i was only making $1.90/hour and couldn't possibly make the payments. so i went back to court and had a different judge who lowered the price to $100/month. years later i went back to court to the 1st judge(who awarded her $250/month) and he told me that the 2nd judge(lowered the payments to $100) wasn't suppose to do that. then he reinstated the $250 a month. and i was told i have to pay all the money in back child support. That's why i want to know is it legal to still be paying back child support on a 35 year old.???