When is it most appropriate to transition from first to senior author? I am transitioning from junior to senior researcher status. I have several publications as first author, many as coauthor, and a few as senior (last and corresponding) author.

As people perceive differently the role of authors according to their position, especially when looking briefly at a scholarly paper, I am wondering when it is most appropriate to transition from first to senior author.

Does it depend on biologic age, academic age, ranking, tenure, or what else?

My field of interest is cardiovascular research, but I think that a general answer followed by some details on the main different academic fields would be beneficial for ACADEMIA readership.
I think in most fields in which author order denotes the relative level of contribution, while people talk about the last author as being the "senior" author, this is more of an artifact of the fact that the PI of the group generally makes the least contribution to the work. I have never heard of some one striving to be senior/last author. Rather, the author order simply reflects the order of contribution.

If I have the highest academic rank, am the oldest, been in academia the longest, have a name that comes last alphabetically, and obtained the funding, but contributed the most to the project, I would want first authorship. More often than not what happens is people in my lab do most of the work and I make contributions through guiding the research. This generally leads me to making the smallest contribution and naturally being the last author even though I have the highest academic rank, am the oldest, been in academia the longest, have a name that comes first alphabetically.

A related question is when do you start structuring your research program such that you make more less "first author" like contributions. This tends to happen naturally as your time for research decreases and the number of projects that you are involved in increases. Typically this means you have enough funding for a small team of research assistants, PhD students and Postdocs.