Jaylen can indeed be a girl's name, but it is just as popular for boys; it is a unisex name.
There are many unisex names today - 'Taylor', once just a boys name is now also popular with girls. Kim (or Kimberley) started off as a male name but is more popular with girls now. Tony is used for girls too with the spelling 'Toni'.
Jaylen means 'One who heals others; one who is tranquil' so that could certainly apply to either gender.
Possibly a male spelling would be Jaylen, and a female would be Jaylyn, but there is no hard and fast rule.
The name is thought to have originated from 'Galen', which was the name
of a 2nd-century BC Graeco-Roman physician who contributed greatly to anatomy
and medicine. That's quite a name to live up to and something to be proud of.