Bokutachi Otokonoko
Where they start out as children and their relationship slowly develops. I loved this manga for the most part, but the ending was disappointing.

I would prefer them to start out as children, but it doesn't HAVE to, just as long as their relationship develops slowly.

Also, no hardcore shota. A simple kiss or two is cute, but i don't like sexual scenes with little boys.

Complex is the only one that I can think of where they start off as kids.... the first chapter has Shota in it but you can skip that (it is basicly just to show how/why their relationship starts off the way it does and it doesn't get too bad I don't think - it deals with a teacher and the other 'friend' rescues him from the teacher). Either way it is a great read and I was skeptical about it at first since Shota is a NO GO for me.... this manga has got to be one of the best yaoi ever written in my opinion. Sorry I am recommending this even though you asked for no Shota... but really you can skip the first chapter and still get a good part of the story.

Dear Green: Hitomi no Ounowa and sequel Dear Green is also a slow paced manga that shows development. No shota here.

Perhaps Kakko Warukute Kakkoii Kimi?

[img]https://31.media.tumblr.com/fed8f641faa089fa16ee883f5b18f006/tumblr_n09tpwWCYW1qk16e0o1_500.png[/img]
K n e e l .... This is the difference between your and my eye-level.
Rai from Noblesse

Tight Rope
Komatta Toki ni wa Hoshi ni Kike!