Enlarge Person on an Eidolon works... or does it?

Okay, so I realize that by the rules I can cast spells with a target of You on my Eidolon with the "Share Spells" ability, but do *I* still need to be a valid target? So, for example if I an Aasimar (and do not have Scion of Humanity) then I still can't Enlarge my Eidiolon?

Share spells has two clauses. One of them is spells with target of "you". The other is that spells which dont normally affect the eidolon still affect it. The eidolon works due to the 2nd clause.

So then I can cast Enlarge Person on my Eidolon even though I can't on myself, or am I wrong that I can't cast it on myself? Remember, I am talking about an aasimar character (WITHOUT Scion of Humanity) so I am an Outsider, not a humanoid.

The summoner may cast a spell with a target of “you” on his eidolon (as a spell with a range of touch) instead of on himself. A summoner may cast spells on his eidolon even if the spells normally do not affect creatures of the eidolon's type (outsider). Spells cast in this way must come from the summoner spell list. This ability does not allow the eidolon to share abilities that are not spells, even if they function like spells.

1. The summoner may cast a spell with a target of “you” on his eidolon (as a spell with a range of touch) instead of on himself.

2. A summoner may cast spells on his eidolon even if the spells normally do not affect creatures of the eidolon's type (outsider). Spells cast in this way must come from the summoner spell list.

These are the two parts of the share spells ability.
Because of part 2, you can cast Enlarge Person on the eidolon. For this bit it doesn't matter if you (the caster) are an outsider, aberration, ooze or even vermin. It looks at the type of the eidolon and the spell, not your type :).

This does have some odd side effects. Like you can cast construct only spells on your eidolon.

I've been checking the summoner spell list, but I'm not seeing any beneficial spells that target constructs only on that list. Probably not looking thoroughly enough.

A samsaran with Past Life Mystic might be able to find some shenanigans...

These same clauses exist for Familiars and Animal Companions as well.

You may encounter the occasional GM that believes clause #2 is an extension of #1, and not a separate clause in and of itself, but IME those encounters (and forum arguments) are few and far between.

Really? So, a witch can cast Enlarge Person on her cat?

a witch can cast Enlarge Person on her cat?

Even Decompose Corpse if they're that way inclined.