JIM HENRY (2nd May):
I'm not sure if

Juna beletan amindumas.

would work, however, and I'm not sure why it seems less
well-formed than the previous two sentences.

ME (2nd May):
Because, I think, we don't know what the adjectives refer
to.  I dare say, one could contrive a context in which such
a sentence might be acceptable, but I think it would still
feel awkward.

EUGENE OH (4th May):
Might the sentence not be parsed to mean "a" youngster and
"a" pretty person? I'm not the most proficient Esperantist
so this is just my interpretation of the sentence.

If one wanted to mean that, they'd probably rather use the
terms "junulo": youngster and "beletulo": pretty person
(-ul- is the personifying suffix). Given Esperantists'
propensity to actively use the various productive suffixes
the language offers, I'd expect that rather than just using
the adjectives without article. The sentence:

Junulo beletulon amindumas.

even with its marked word order, is at least completely
well-formed and immediately understandable, and actually
nothing very special at all.

Yes, "a youngster is wooing a pretty person" much surely be, 
as Christophe writes, _Junulo beletulon amindumas_ (or those 
three words in another word order) - and that only if the 
two participants are both male.  In my original sentence, 
many emails back, the person being wooed was a _fraulino_. 
If we want a heterosexual courtship it will be _Junulo 
beletelulino amindumas_ (or, of course, Junulino beletulo 
amindumas). A lesbian courtship would yield _Junulino 
beletulino amindumas_.

But the more I think of _Juna beletan amindumas_, the more I 
am convinced it is an incomplete sentence and, therefore, 
ill-formed and, at best, ambiguous if not, indeed, 

Thinks: Do you require -ul- if you also have -ino? Or am I 
being misled by Ido?

Nid rhy hen neb i ddysgu.
There's none too old to learn.