i'm looking for manga where there is an elementary/middle school girl with voluptuous body, for example: Cyclops Shoujo Saipu.
H or Bordeline-H is fine

Usa Mimi from Kodomo no Jikan comes to mind. Elementary schooler who is definitely ahead of the curve when it comes to puberty.

I can throw in a bunch of H entries once I get home from work. Though since you will be getting a bunch of H answers to this query, the 18+ section might be the right place for it.

Edit:
Ah yes., Mahou sensei Negima! Some of the girls in the class 2-A are pretty damn busty and otherwise physically mature, yet they are all supposed to be 14 or 15. Oh.. You did have that on your lists.

[img]http://i2.kym-cdn.com/photos/images/original/000/028/438/5700.necropost4kobf7.png[/img]

Maybe...
Rou Kyu Bu!
Btooom! (she's supposed to be 15)
Lotte no Omocha! some side characters maybe

owh i forgot about Usa Mimi, yeah that's one of my favorite manga. even if i post to 18+ section, there's rarely any reply, and i don't only search for H manga.

i'm not aware Ro-Kyu-Bu! have a manga, but i already watch the anime. thanks for the suggestion, i try read Btooom! first.

any other suggestion?

Right then.. all of the below will be H entries. So ware ye well a-fore clicking any of the links below. Thar be PORN! ahead. You have been warned, dammit.

Kemomimi Onsen e Youkoso One guy, two animal-spirit lolis, one of 'em has large breasts.
Imoten The girl in the first set of chapters has quite the body for someone on the 6th grade.
Pretty much all works of KAHLUA Suzuki feature Junior-High girls with well developed bodies. The works lean toward.... forcible copulation. Nothing really violent, but no consent either.
Zettai Kengen Sisters! The youngest of the 3 sisters is still in junior high, but has booty both up and below.
The comedic entry The Secret Spot Behind the Shinto Shrine 5th grader with serious torpedo-tits.

[img]http://i2.kym-cdn.com/photos/images/original/000/028/438/5700.necropost4kobf7.png[/img]

Tonari no Raenzel W - not H nor Borderline…

whew... thanks for suggestion, well i don't mind thougt about Hentai manga, i like Imoten, not only lolicon but there's an incest too.
for additional about H manga, i remember another manga, try Oh! Imoto

H manga
Try Lovable-oneshots
Idol sister-the imouto/idol was super cute, 2 different stories
Bishoujo Sister Koakumakei-one shots
Rori ana-one shots

Manga
Cherry x Cherry
Yomeiro Choice-

he screwed with everyone, even with his future daughters

Oniichan Control
Sakuranbo syndrome-meh, elementary body

[color=violet]Tournament Round 1[/color]
[color=blue]Round 2[/color]
[img]http://i.imgur.com/CcwHreL.png[/img][img]http://i.imgur.com/aQ0E4sC.png[/img]

Oniichan Control

How do you figure? The OP was for elementary or junior high girls. Every character in Oniichan Control is way past that age, including Noa. The series begins with her taking, and passing, college entry exams.

[img]http://i2.kym-cdn.com/photos/images/original/000/028/438/5700.necropost4kobf7.png[/img]

Uhh, yeah, haha.. Sorry bout that, she had a loli body though, I think.. 🤣

[color=violet]Tournament Round 1[/color]
[color=blue]Round 2[/color]
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Quote from Knightzomegaz

Uhh, yeah, haha.. Sorry bout that, she had a loli body though, I think.. 🤣

Which is the exact opposite of what the OP is about...

[img]http://i2.kym-cdn.com/photos/images/original/000/028/438/5700.necropost4kobf7.png[/img]

In Mysterious Girlfriend X, the Female MC friend is Highschool with looks/heights like grade school but has voluptuous body/breast. And she wear glassess.