I think the only FTP history you would find is in /var/log/messages*. Depending upon how your particular OS rotates the logs, you might find the info in /var/log/messages, /var/log/messages.1|2|3|4, /var/log/messages*.tgz.
On a typical CentOS server, for instance, you have about 1 month worth of /var/log/messages* logfiles. They rotate weekly. /var/log/messages is most recent, /var/log/messages.1 is a week older, /var/log/messages.2 is two weeks older, etc.
So if you know the username, I would attempt to do this:
grep username /var/log/messages*|grep logged -- where 'username' is the particular username you are interested in
That will give you a list of the dates/times that a particular username has logged in. Now, if that user hasn't logged in for over a month, you aren't going to find it in the logs on CentOS. [Your OS install may differ with regard to how long logs are held / rotated].
M