Kallman's Syndrome

 Kallman’s syndrome is a biological condition caused by the lack of
GNRH producing cells in the hypothalamus of the brain.  Without GnRh
hormone the pituitary gland does not produce LH or FSH hormones.  
Without these hormones the individual will not experience puberty.  
Thus they are unable to have sex or produce children.  Various
secondary sex characteristics such as pubic hair, voices changes (for
the male) and other secondary characteristics will not happen.  With
modern medicine and hormonal replacement therapy those with this
condition can go through normal puberty and sexual development and
sexual function is no different than those who do not have kallman’s
syndrome.  Also, fertility is typically possible although not guaranteed.  
For more information click
here or here

As additional information… this Side A website describes a eunuch this

“R. Joseph said: It must have been such a saris [eunuch] 6 of whom I
heard Ammi saying. 'He who is afflicted from birth...’ Our Rabbis taught:
Who is a congenital saris [a born eunuch]? 13 Any person who is twenty
years of age and has not produced two pubic hairs. 14 And even if he
produced them afterwards he is deemed to be a saris [born eunuch] in
all respects. And these are his characteristics: He has no beard, his hair
is lank, and his skin is smooth. R. Simeon b. Gamaliel said in the name
of R. Judah b. Jair: 15 Any person whose urine produces no froth; some
say: He who urinates without forming an arch; some say: He whose
semen is watery; and some say: He whose urine does not ferment.
Others say: He whose body does not steam after bathing in the winter
season. R. Simeon b. Eleazar said: 15 He whose voice is abnormal so
that one cannot distinguish whether it is that of a man or of a woman

For the full article please click here.   The description above matches up
in many ways with kallman’s syndrome .. lack of beard .. lack of pubic
hair .. abnormal voice (no voice change in puberty) etc.  It would also line
up with someone whose testicles are not functional from before puberty
either due to a medical issue or castration.  So I don’t see how this
corresponds to being gay.  For a plausible explanation of the possibility
that some eunuchs may have been gay please click