The fruit in your picture does not look like a cucumber to me, the spanish green ones probably are. 5 inches long should be the best size.

It looks like what is sold here as Lemon Cucumber, actually an edible gourd. Cricket ball to softball size is usually best.

I just had a thought: do you folks play softball over there?

I am not familiar with this one, and haven't played softball for years. LOL.

hi
have asked the person who gave me plant and they bought it from garden centre under the name of...apple cucumber!!!??

Whoa! Not what I thought it was! Sorry, I really don't know how big it should get.