i’d opt for [name_m]Emrys[/name_m], i love his soft and rare sound and “immortal” is an amazing meaning for an old soul of a babe 
though you’ve likely thought of this, i feel like [name_m]Rhys[/name_m] could be a nickname for [name_m]Emrys[/name_m]! 
i’ll also throw in [name_m]Aquila[/name_m], [name_m]Finnian[/name_m], [name_m]Oren[/name_m], [name_m]Evermund[/name_m], and [name_m]Rowan[/name_m] 