When can a senios citizen that is 89 years old get to stop paying taxes ?

The person's age is irrelevent when it comes to paying taxes.

The determining factor on paying taxes is the amount of income earned.

A newborn baby whose parents use him as a model and earned modeling fees of $25,000 MUST pay taxes on that money. Granted, his parents will file the return and pay the taxes, but the return has the BABY's name on it.

Same logic applies to the senior citizen. If the 89-year-old is reciving interest and dividends from his investments and they exceed a set threshold, a tax return is required and taxes must be paid. I currently have several clients in their 90s who have to file a tax return and mail a check every April 15th, mosting due to the dividends they receive from Merck, ExxonMobil and Proctor and Gamble.