If the editor handling my paper is a retired professor, then would it be fine for me to inquire about my paper status? I have a paper under review at a journal for 2.5 months. 

Given: 1) it is a short paper taking only two pages, 2) I know that the editor handling this paper is a retired professor, and 3) I have submitted several short papers (the number of pages is &lt; 5) to this journal and all of them were handled by this editor. Yet according to the past events, 1 month is the longest for a first decision. Then if it is fine for me to send a polite, short email to inquire about my paper status in order to "remind" the editor?
The time frame to a point where a question can or indeed should be sent varies depending on the typical time for that journal, or of similar journals in your field. To me 2.5 months does not sound too long, a decision after one month sounds very quick if I consider a normal set of reviewers also should make their evaluations in that period.

If you think sufficient (relative to what you perceive as "normal") time has passed you can certainly send a short e-mail asking for information. If you have an excuse for asking, in addition of just wanting to know, your mail is far less likely to be perceived as "pushy". But, regardless, editors will get hit by such mails fairly regularly and despite some of them or the bulk of them being a source of irritation at times, the question is not strange by any means. It is all down to the tone of the mail.

The fact that the editor is retired should not affect any aspect of the review procedure so I do not see any reason to take that fact into consideration. The journal must appreciate the work the editor is doing, otherwise the editor would likely not be there.