Yep, I’ve had the same experience with my cascade over the years. The top cones ripen sooner. Personally, I only pick as they’re ready. This year, for whatever reason, I have one bine that’s 1-2 weeks ahead the others. In fact, they should be ready to pick in the next few days. Planning to brew my annual 10 gallon batch of wet hop ale with the rest of them in a couple weeks.
Chopping the entire plant down and harvesting all at once is a commercial practice. Hand picking for the big guys is laughably impractical. Depending on the individual setup, we home growers have the advantage of being able to harvest as they come ready.
Hand picking without cutting the plant down is completely viable for us and generally better for the plant health. After the harvest the plant has a month or longer to send energy down to the crown. The one thing I will do sometimes, if a bine is high up and hops just out of reach, I’ll cut off a side arm to bring down for easy picking.
Regarding those younger hops low on the plant, in years past I’ve harvested them all the way into October. Maybe just an oz or two dried, but a bonus you won’t get if you chop the whole plant down in August.