but most sources say that
gil-galad was born in the eldamar. According to the majority of sources, gil-galad was born in Eldamar
It is written in already another version that gil-galad's mother is a
sindar elf of the north. I personally think according to the majority of sources, gil-galad was born in eldamar.
Most sources do not say he is born in Eldamar. There is one variant that has Gil-galad born in Eldamar. That variant is from about six years before
Orodreth is Gil-galad's father. In other variants where
Finrod is his father or
Fingon is his father he is an "elvenchild" or a "young son") when he is sent to the Havens. (and in the Finrod variant his mother is noted as of the folk of Eglorest, i.e
Cirdan's people). While in the variant which has him of unknown parentage born inYT 1481 notes him as 25 10 to 20 years into the the
Second Age. Meaning he only reached 'maturity' in the last century of the
First Age.
None of those sources indicate him as being of age to go off to war (which seems to be your intent with your question).
Now you have several options. He is the son of Finrod, with a
Sindarin mother of Eglorest, and hence born in
Beleriand and still an 'elvenchild' when sent away; or the "young son" of Fingon, with an unknown mother; or the son of Orodreth with a Sindarin mother (and hence born in Beleriand); or he is born in Eldamar, of unknown parentage, and still immature until the last century of First Age.
Alternatively, you can just make up your own version of Gil-galad (like your cited wiki seems to do), in which case he can be whatever age you want and fight in whatever
battles you want.
So, what version of Gil-galad are you asking about? Your version or one of the variants
Tolkien wrote about?
edit:
The Tolkien Gateway article you link to in response to
@Aredhel Ar-Feiniel is incorrect. It is not the "probable birth date of Gilgalad, the son of Orodreth". As noted above, Gil-galad as the son of Orodreth is from ca. six years later and has a Sindarin lady of the North as his mother.