You could (in my opinion, unfairly) describe yourself as:
- Retired because of age or infirmity
- Too old for use, work, service, or a position
- Antiquated or obsolete
Collins Dictionary: Superannuated
While it doesn't specifically address computers or an inability to learn, it does capture the general feeling of "being unable to adapt to modern technology".
For what it's worth, I don't believe this does apply to you. If you have a look at this study on the distribution of computing skill, being able to get here and ask a question would put you as at least a level one (which would put you ahead of ~40% of adults in OECD countries), maybe the lower end of level two. Having a desire to learn goes a very long way...