Why did Luc age?

[Voltaic]

The most probable theory is that he aged because he wanted to age. I have also thought that a rune bearer could possibly age when needed so they could be at a prime state for the situation they were in, but you can't really be sure unless someone could get younger.

It could be that he never aged at all though, the art style and clothing he wears effects how old he appears. The clothing and over all look didn't really change between games 1 and 2, so he didn't appear to have aged. The only thing that made him look slightly older was the clearer more proportionate art style of game 2. In game 3 his hair style and clothes changed a great deal, which was a more mature look, making him appear older. It’s understandable that he would update to a mature look, at his status he wouldn't want to look very young.

[Maldonado]

Well said! He is a wizard after all, so it is possible he did not want to age simply because he wanted to look like an innocent child, thus fooling his opponents who might underestimate him because of his appearence.

[Hugo]

This is what sars said on suikox about Luc's aging.

True Rune bearers who acquire them when they are young MAY age to the point of about the appearance of 16 years in age. Anything above that means there would be no further aging. However, aging under the apparent age of 16 also depends on the rune and the bearer's will.

[Fayt]

Maldonada: I think he never aged. He looked just the same in all 3 Suikoden games, the only thing that made him look younger in Suikoden 1 was an artist's style of drawing that was completely different then those in Suikoden 2 and 3.

I agree.. The artist drew different and the graphics when suikoden 1 was created then 2. Not as good as graphics today..

(Tir McDohl (Suikoden 1 Hero) (Sould Eater trun rune if I remember right) Also looked different in Suikoden 2....
And Ted.. Suikoden 1 and 4..)

I think it was just the skill of the artist(s), the tools they had, and how devolpoed the technology was.....

[Maldonado]

Indeed. If I were a wizard or something like that, I'd deffinitly want to look like a 16 years old boy rather then some old geek with white beard and pointy hat...