Why is it so important to know?
If it's really important why doesn't anyone ask the admin or owner about the launch date because it's much more accurate than having to rely on a different site.
I did not say it was important to know, nor that it is important for the legitimacy of the site. My question was purely informative.
It looks like those
sites don't know how to make a proper investigation

AFAIK, Roobet was officially launched in late 2019. Almost around the same time when this thread was created.
It's true that the domain name roobet.com was registered in 2016 but if you check this archived version from 2018
https://web.archive.org/web/20180808191435/http://roobet.com/ you will see that the domain was offered for sale back then.
absolutely-positioned's earliest posts, especially this
one, confirms the above.
Thanks, that's exactly the information I was looking for. It appears the first tweet by @Roobet was posted on November 27, 2019, which confirms the story.
https://twitter.com/Roobet/status/1199730854269861888