As @fixer1234 implied, it could be possible depending on the settings of SSH, how weak the password is and how vigilant the intended victim is, but its not likely.
There are a large number of ways of frustrating SSH Brute force attacks, including by eliminating passwords altogether (and preferring public keys, in which case, unless you have access to the multiverse and god-like control of time, you are SOL), refusing root logins, only allowing logins from given IP's - or even different given IP's for different users, banning IP's attempts after a few tries etc.
If you have access to the victims system aleady, and have the shadow file (ie hash of the password), your chances are a lot better as you are not constrained by network limitations, and can throw a lot more CPU at the problem - in which case, depending on his password this falls into the realm of practical in many, but not all cases.