This is an example of personification. First, in this quotation, Romeo is attributing human motivations to the "stony limits"—technically, he is referring to the walls around the Capulets' home, but the word "stony" can also be applied to a person who is rigid or unyielding. Romeo is saying that these walls, or strict people, cannot "hold out" love (which also implies that they would attempt to). The stony walls are an outward reflection of the disapproving Capulets.
Meanwhile, love itself, an abstract concept, is personified, imagined as acting almost under its own power to try and break through the limits that have been imposed upon it. Love itself cannot "attempt" anything; arguably, love could cause Romeo to attempt something, but on its own, it is not capable of action. In this piece of dialogue, however, love becomes self-motivated, something which is capable of doing whatever it dares to try and will not be restrained or constrained by physical things which work against it.