What can cause an inflamed spleen for an 81 year old? can it heal on its own? any dietary treatment?

I not aware of an inflamed spleen. It can become congested or enlarged by response to infections such as mononucleosis or malignancy or by bleeding into it from injury or by cirrhosis of the liver.

Spleen is most of the time enlarged due to conditions such as infections or liver disease, for example, not commonly affected itself. Recommendations can only be made once the source becomes apparent.