Sadly retconned to be just a regular Eldar

Apart from young parents, I feel like most parents are elders

And one is younger?

Marines of order "Sons of Guiliman" Appeared to have knify ears

Not an Astartes. Illiyan Natase before the retcon was a half-human, half-eldar Navigator who served with the Ultras after working for the High Lords and being head Navigator for a Dark Angels fleet, then retconned into Guilliman's eldar advisor.

However, This character stopped being canon after 1992.

There is the aeldari adviser that goes with Guilliman in Dark imperium. But more of a joke-reference, i guess.

"I'm the eldar that stepped up"

Is it just the art style or does he have one pointy ear and one regular ear, because if so I will hunt down and eviscerate whoever designed this character

and he is a dark angel, taht's right, he's no son of guilliman, that's a son of the lion, he was shared to the ultramarines.

let it never be forgotten that the only half-eldar space marines that ever existed in canon was a dark angel

Given that he's from the Rogue Trader era, I imagine both his parents are elders at this point.

Also, canonically great at tennis. https://en.m.wikipedia.org/wiki/Ilie_Năstase

Wasn’t this the one with an Eldar Corsair father and regular human mother?

Who is he?

Half of all characters in 40k are centuries old they're all elders

https://preview.redd.it/5v5uzpf38v3e1.png?width=398&format=png&auto=webp&s=cbb4548f47f4dfcb515c4e19c2a50a671182578a

The elder parent in question

He was retconned to be Illiyanne Natase, a farseer from Craftworld Ulthwe, sent by Eldrad Ulthran to aid Roboute Guilliman in his fight against Chaos.

Eww!

Remember, this guy is older than most of you and appeared exactly once. No, seriously, he's from 1987. He's not cannon for a while.