The full context is needed. In order to give a complete answer.
It may be similar to "easy prey" or "no easy prey"
1."easy prey" = somebody that is easy to deceive, prone to being taken advantage of.
1a. "easy prey" = an animal or creature that is easy to catch.
2. "no easy prey" = somebody who is hard to take advantage of, or refuse to be taken advantage of.
"no tender prey" = I am guessing may be referring to a person who is not like a young person easy to take advantage of ?