This seems to be referring to the health issues we get in our body as we age. Joint issues can refer to arthritis, and it appears that the eyesight has worsened. Other things seem to have happened to the person as well. Despite all the natural problems we get as we get older, this person seems to remain happy. The other person seems to want to know how this person can remain happy while having multiple health issues along with the possibility of obtaining more health issues.

The sentence is incomplete. It might say, "it’s not as though you’ve been spared all the afflictions of prison life.". Prison life has many afflictions (prisoners are afflicted). Some prisoners are afflicted less: they are spared some of the afflictions of prison life. Some prisoners are not afflicted at all: they are spared ALL of the afflictions of prison life. If you are not afflicted, then I can say "You have been spared all the afflictions of prison life". However, if you are afflicted, then I cannot say that. It is not like that: it is not as though you were spared. The opposite of this sentence is simpler: "It is as though you have been spared all the afflictions of prison."