In prison if you have a gang affiliation it's important to show your colors. For my older inmates---over age 40---that would be grey.
In general older inmates are respected by younger inmates. They make good cellmates because they're not considered a threat and because they may have some good advice to offer. They're quieter and less annoying than young cellmates who are busy yelling to their friends down the tier.
Chronological age and physical age aren't always the same. The street lifestyle can add ten to twenty years to one's physical age. In between the substance abuse, head injuries and HIV dementia there aren't a lot of young neurons in my outpatient clinic.
By policy every inmate is required to have an annual physical. Beyond a certain age they also start screening for dementia with an annual Mini-Mental State Exam. Neurology consults are available and you can also do the basic dementia related laboratory work. Inmates can be sent to outside institutions for brain scans if necessary.
The biggest challenge in carrying for elderly inmates is the need for nursing services. No general population tier has nursing staff to supervise showers, dressing or feeding. Elderly prisoners with mobility impairments are at risk of falling because correctional facilities just aren't built for fall prevention. There are no geri-chairs or vest restraints or non-skid rubber mats in the showers. My most memorable fall-risk example was of an elderly inmate with Parkinson's disease shuffling along in leg irons with untied shoes. It was enough to make a geriatrician cry. (I did make sure his shoes were tied before returning him to the tier.)
Some jurisdictions have options for special parole for elderly prisoners. You usually have to document that the inmate has a six month life expectancy or else is too incapacitated by disease to pose a threat to society. Of course, whenever you do that you run the risk of being wrong. Our most famous case of a wrongful lifespan estimate involved Deidre Farmer, a transgendered inmate with terminal AIDS. (Mr./Ms. Farmer was best known for his role in the landmark Supreme Court case Farmer v. Brennan, which established the mens rea (mental state) standard necessary for a facility to be found "deliberately indifferent".) Farmer was granted a medical parole and promptly went on to get better and commit new identity fraud offenses. He was ultimately apprehended after trying to forge his own death certificate.
So elderly folks with antisocial personalities can still be antisocial; they just do it slower.