One of the most obvious suspicious signs for bots and fictive profiles is the age of their profile. 1st level connection can see when they connected to each other, but it is not possible to see when a user (both connections and not) opened an account.
To find this info, or at least understand whether it is a new user or not, we will need to use the unique ID number that LinkedIn associates with each profile. Fortunately, the users’ IDs are created in some chronological order (a larger number indicates that the user is newer), and therefore, by comparing the user’s ID with other user’s IDs that we know when were they created (it is also possible to open a new account for a reference), we can know more or less what the age of the profile is.
In order to find the unique ID of each profile, we will enter the source code of its profile (ctrl+u when on the user’s profile page), and look for – ‘urn:li:member‘, we will get over 100 results, while most of the first ones being your profile ID. To locate the ID of the profile we are looking at, we will look at the latest results we got in the search (click on the previews results button to easily get the last results).
Another option is to search – ‘followingType‘, and the number that will appear before is the ID of the target.
Now, all that is left is to compare with other IDs we have, that we know their joining date (you can try to create a list of profiles you know when they were created, by months and years, and try to get a more accurate estimate of the joining date.