I’m not saying there are no 60-year old illiterate people. Of course there are and the examples you quote are among them. What I am saying is that they do not exist in the huge numbers that can be found among much younger adults.
Some of the work that I do involves meeting people of all ages and from all social classes. All are asked to read some simple documents as part of that work, many are also required to write a small amount. I meet about 200-300 people per year whilst doing this work. I rarely, if ever, encounter a person aged above about 50 who is what I might describe as “illiterate” (that is, cannot read a simple document and write a few words). Conversely I come across large numbers (probably at least one in ten) of young people who have not mastered these basic skills.
Not very scientific and very anecdotal, I know, but a good guide as far as I am concerned. It’s always easy to find statistics to support a particular contention, so look at the table on page 11 of this document:
http://www.parliament...rch/rp99/rp99-111.pdf
“Approximately 100,000 school leavers (16%) leave school every year unable to read, write and spell adequately for the demands of daily life.”
“In 1974, around 2 million adults (6% of the population) had insufficient literacy skills to cope with everyday life.”
Yes, these two measures are different and of course 10% of people in 1974 could have improved their literacy skills since leaving school, but it seems unlikely. There are further difficulties in making comparisons over a long period because the definition of “literacy” has changed considerably. So it really comes down to anecdotes and experience and a far smaller proportion of sixty year olds I encounter are illiterate when compared to those who are much younger.