Trying to figure out elven/half-elven genetics here... more or less thinking out loud.
It makes little sense to me that Elwing reaches physical maturity as quickly as Eärendil does.
Let’s look at their family trees:
Eärendil = Idril (female elf) x Tuor (male Man)
Elwing = Nimloth (female elf) x Dior (male ?)
Dior = Luthien (female maia/elf) x Beren (male Man)
Luthien = Melian (female maia) x Thingol (male elf)
It may be accurate to call Elwing half-elven, but her other half is both Man and maia. So while it’s not impossible that she inherited a growth pattern more like that of Men, it should be less likely - particularly since genes suspected or implicated in growth/puberty/etc are found on multiple chromosomes. Yet Elwing is physically mature enough to bear children in her late twenties, while elves don’t normally hit puberty until around fifty. (On a related note, how long was her pregnancy? The elven year, the Mannish nine months, or somewhere in between? So many questions!)
With Eärendil it's somewhat more logical that he matures faster than elves - the Man in his family tree is a father, not a grandfather, so he inherits more mannish genes. It makes sense to me that he ends up with a growth pattern that may not be as quick as men, but is significantly faster than elves. Incidentally, this also applies to Dior, who canonically matured at a faster rate than elves as evidenced by him married and having children in his thirties.
Also, please note I’m talking strictly about growth/maturity patterns, not mortality. The only one of these half-elves I think would be mortal is Dior, since his parents were both mortal* when he was begotten. But Eärendil and Elwing were both born to elven mothers, making the matter of their mortality a lot more questionable. (And canonically, this is an open question, as Ulmo pointed out- “say unto me: whether is he Eärendil Tuor’s son of the line of Hador, or the son of Idril, Turgon’s daughter, of the Elven-house of Finwë?” The same question can be asked, albeit with different names, for Elwing. And faced with that question, the Valar punted - they had the half-elven themselves decide!)
*Luthien chose Beren’s fate, not his kindred. She was still an elf/maia, just with the singular gift of being able to die a mortal death. I also wonder if she is the only elf who could have been granted such a fate, due to her maiarin heritage - the ainur who entered Arda stay within it, but they are not bound to it in the same sense that the elves are.