https://exhentai.org/ probably has the most extensive catalog of yaoi (and all sorts of doujinshi, really), but there's a process required to access the website. Here's a guide to accessing it: https://www.reddit.com/r/hentai_irl/comments/5w73k9/how_to_access_sad_panda/

I also recomend exhentai, but you can use https://e-hentai.org/ until the process is done, it's the same with just some less content but still a lot

Yup, https://myreadingmanga.info/genre/bara/ is a great start but there's a lot out there.
http://www.mangago.me/genre/Yaoi/
http://www.yaoiotaku.com/forums/threads/25768-sekaiichi-hatsukoi-nakamura-shungiku-%5Bjp%5D
http://www.yaoiotaku.com/read-yaoi-manga-online.html

Thank you for the links. Some have very good content. Some nice art works can be found on pixiv too.
Unfortunately most of the Doujinshi & Manga arts and games websites I checked don't ban explicit underage content.
So these are not an option to me.
BTW, porn arts involving unambiguously underage boys and girls are illegal in most of western countries.
Are there any good sexually explicit Doujinshi & Manga websites which ban underage content?

PS: Is there a japanese word equivalent to "twink" clearly excluding underage boys?

http://www.mangago.me/genre/Yaoi/

http://www.yaoiotaku.com/forums/threads/25768-sekaiichi-hatsukoi-nakamura-shungiku-%5Bjp%5D

http://www.yaoiotaku.com/read-yaoi-manga-online.html