A lot of hikers start their long hikes very early, with the thought that they will train on the trail. On the PCT (Pacific Crest Trail) that means they may run into snow in the first 150 miles. Then, many of them start skipping right away, setting the tone for the rest of their hike.
You also don’t heal as well on the trail as you do at home where you can, sleep comfortably, take baths, eat good fresh food, and hydrate well. The trail has stresses that make it hard to fully rest and recover.
A smarter alternative to starting early is to stay at home for those two or three weeks and do training hikes of 20 miles every other day with a 35-40 lb pack. Get good rest, eat good food, take baths, heal and build in a stress free environment. Then when you hit the trail with your light pack, you will be ready to go.