When you say single sitting, it is not quite clear whether you appeared for all the 3 years subjects at the same time or it was a condensed 3 year Bachelor's programme into 1 year of study. According to an article available at the official website of OU, https://www.osmania.ac.in/AcademicInfo2012/Courses22008.pdf , it says:

"A candidate who has obtained his/her degree of post graduate degree by single sitting upto the year 1998-1999 may be treated as eligible for admission into Law courses according to Bar Council of India".

Now there are 2 things to it. This states that Single sitting upto 1998-99 and it is only available for those Candidates who have completed their PG through Single setting. Now you completed your Bachelor's in 1987 but you have completed your BA and not Post Graduation. There are Institutions that have no upper age limit but they need 3 year Bachelor's degree and single sitting might not be an option. But if you are fine with Distance Education courses, you need to remember that LLB through Distance Education is not considered eligible to practise Law in India. So if practising Law is what you are considering, unfortunately, that option is not available for you. But you can still study LLB through Distance Education.