{original post had no questions}

"But we *don't* have to follow the US Navy command structure, or
faithfully capitulate the command structure of ANY historical service.
B5 is a fictional universe. And I maintain that by the internal logic
of that fictional universe, a younger captain would not entirely be out
of line."

Speaking as the guy who made up that internal logic and that
fictional universe...there is a profound difference between the
examples you were citing from the Revolutionary and Civil Wars and the
situation in B5. To command a starship you have to have experience in
combat situations, and also in how to be level-headed enough to talk
your way out when you have to. The average career military person may
enter at 18 years of age, or wait until finishing college or OTS
(Officer Training School) at 20-21. You may enter respectively as an
ensign, or as a Lieutenant, and be assigned to your first unit at that
point. This has nothing to do with any particular country's military
scheme as simply with the math involved.

Promotion in EVERY military is based in large measure on combat
experience. (Which is why women officers are fighting so hard to get
access to battlefield postings.) Working your way up the ranks simply
takes *time*.

There's a profound difference between an Air Force captain, who
is responsible only for his own plane, and a Captain of a large vessel
who must command a staff and be responsible for the lives of hundreds
of crew members. Before they will entrust you with that responsibility,
you have to have proven yourself over the long-haul. This is all the
more true with something like B5, where the CO also operates as a
military governor of sorts. With a quarter-million lives on the line,
a person in his or her 20s simply does not have the years of experience
required for the job...and there is no way to gain that experience
other than with time. It's not strictly a question of maturity, it's a
question of experience as well, and the bureaucracy that comes with
*any* military structure that says "you must pay your way, and earn
your stripes."

Just because something is SF doesn't mean we must throw away
*external* logic in our attempt to make the *internal* logic into
something just because we want it to be so.

jms