I know that it is fine to edit old posts, especially if the edits help e.g. accessibility and readability. But should I do it a lot? @gotube has edited a lot of old posts, but @gotube is a moderator and has been here for around 2 years, so I'm assuming normal users should not edit as much?
To see if only moderators do the bulk of editing (they do not), view this page
Editors: Ranked by year: @gotube♦ is listed in second position. Admittedly this does not show how many of those edits were performed on old posts but it gives an idea of users' housekeeping efforts.
I'll quote from another moderator's answer to you last week:
I can't imagine anyone complaining about too many old questions on the front page. . . . This is unlike edits to old posts, which have limited value, so they need to be done in moderation.