My wife and I climbed Mount Greylock last weekend. It is a beautiful hike, and the views are truly breathtaking. We started on Hopper by Haley Farm and went up to the summit which was 4 miles. When we got to the summit we planned on eating lunch. That was a mistake because the restaurant was closed for a private function. The take out had a 30 minute line, we should have brought food with us just in case. We did bring water.
The trail is steep and at times very wet. I would suggest really good hiking shoes or boots not sneakers. You will be waking through runoff, mud, loose rocks and lots of leaves. The better your footwear the better you will be.
I would suggest you consider a staff or trekking poles. This will be very helpful coming down as there are some really treacherous parts of the trail. I also suggest you allow enough time so you don't get caught in the dark.. My wife and are 60 and it took us 2.5 hour to reach the top. We came down Haley Farm trail (5 miles) which was about 3 hours.
There are other trails you can take and it might be worthwhile to research which trail you want to take. Alternately you can drive to the top or drive halfway and then hike.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.