Welcome back to the world of bike!

Not sure what your LBS was trying to tell you - by me, your leg should be almost straight at the bottome of the pedal stroke with no rocking of your hips while pedalling. A good rough guide is that your leg should be fully straight with your heel on the pedal at the bottom of the stroke. When you ride, the ball of your foot should be over the pedal axle, which gives you a bit more reach so your leg will be not quite fully extended at the bottom of the pedal stroke.

Hope that was clear enough to be helpful.