Went a few weeks ago with my husbands and 3 kids ages 16,13 and 10. It's just under a mile mostly down, which means mostly up on the way out, but it's not bad. Unfortunately it wasn't a waterfall...just a trickle, but it's a very pretty hike and we were glad we did it.
This is a great family hike. We've done it with kids as young as 6, who did beautifully. The waterfall is a nice destination, but sometimes dull if there is no water (remember the drought? ) But if you really want to challenge yourself, continue on the trail about another mile where you will come to a campground (for backpackers)....
Castle rock is beautiful. You don't really have to be in that good of shape but the choice is yours. there are many paths that will suit your level of activity. Its just beautiful in the winter .....just watch out for the poison oak.
This is a little park tucked away in the Los Gatos mountains, easily accessed by car. The hikes are only moderately strenuous, but offer everything from rocks you can scramble up to vistas as far as the eye can see.