Hey! There are so many great hikes! Have you checked out the All Trails app? It will show you all the hikes near you, number of miles, how to get to them, and more! A couple of my favorites are the Nicholas Flat Trail and Horn Canyon Trail. Happy hiking!
Piedras Blancas trail in the Sespe and just about ant other in the vicinity, although it is a bit warm right now
Not technically in ventura County, but there is fine hiking on Santa Cruz Island and fairly short hikes on Anacapa Island.