Currently aging,senescence and gerontology are all in use covering pretty much the same questions. This seems redundant, so I'm intending to merge them into one tag in the near future. Does anyone have any preference as to which seems most suitable?
These terms are slightly different.
Senescence is the biology of ageing of organisms. Gerontology usually refers to the senescence of humans specifically, and also covers psychological and social aspects. I don't think it's useful to cover human ageing specifically, and the other parts of gerontology are off-topic for this site.
Ageing could refer to either of the above, but also to ageing of, say, a theory. Senescence is unambiguous, and also a more scientific term.