Lyn can promote as early as chapter 24/26.
And nothing you can say can actually change her ability to promote at chapter 24/26. Of a 33 chapter game. Without counting Gaiden chapters. Which FE7 has more of.
Which means, no, don't post the reasons why Eliwood is promoting sooner. It's not what I asked for, I don't care, and it's not what I want.
Fact of the matter is, if you want to like Lyn over Eirika, you can say that Lyn can promote 78% of the way into the game where as Eirika promotes 80% of the way in the game.