I've seen a few of mangas with a character that at first looks like a kid or tween but is actually older than you think. (Like, looks 16 is actually 26) I'm particularly interested in this being important to the plot of the story. Like a 30 year old guy that looks like a high schooler and falls in love with an actual high schooler so he poses as such just to stayed with him. Or a 25 year old is believed to be a lost kid who is 10 years old and instead of saying who he really is he plays along. I just find fascinating the idea of is not what it looks like. Some examples of characters like this are: 4l6u6n

Kirepapa

Even Mitsukuni "Honey" Haninozuka from Ouran High School Host Clubeven though is not yaio (which is a shame)

It's not quite what you're seeking, but for 'posing as' or 'playing along', try:
Bluish Spring" (Chapter 4).

Maybe similar to the examples you've listed are:
"Not Equal.

Other suggestions I might have are stories involving supernatural characters (e.g. vampires who are able to retain their youthful appearance irregardless of the age of time) or works where the mangaka may be actively avoiding a "shotacon" label by specifying that the character resembling a child is actually an adult... So, the discrepancy between the age and appearance of a character may no longer be central to the plot...

Perhaps you might have more luck browsing here.

I liked the idea on Devil x Devil of becoming a child. Bluish Spring was interesting. Hana mo Arashi mo (chapter 4) was more of what I've been looking for though I want a more complex plot.
About supernarural I'm fine with that. About the avoiding the shotacon label is not what I'm looking for specifically but if there are really good ones I would be pleased if you shared them.

Hmm, with a few exceptions (such as two of those already mentioned), I tend to stop reading yaoi where characters are or look too much like children, so I may be at a loss with regard to providing other relevant suggestions.

Maybe:
Saikyou Kyoushi - Kyoushi mo Iroiro Aru Wake de (better story/plot)?

If I think of any others that may loosely fit your request, I'll come back to add to this reply/thread.

I love Hanyuu-sensei no Ryou Sekatsu. Is one of the yaoi that got me obsessed with the whole idea of older than he looks.

Hello
there's also Koibi

/edit/
and also Solo Sex

I'm not a lolicon