Yes, juvenile rats respond better to tickling and tickling just after weaning will get the best results. Starting tickling past 3 months of age is harder and there is less research on it.

That said, some rats just don't respond well to tickling so if you see obvious negative behavior after 2-3 sessions then you should stop trying.

Source: Recently certified rat tickler (proof: https://imgur.com/rzdvf61)