In what way was Jonas handicapped by his early departure?
After Jonas watches his father euthanize the smaller of the two twins, he is devastated. His entire perspective on his father and his life in the community changes. Jonas refuses to go back home. He sees the hypocrisy of the society he has spent his whole life in. He begins to understand that release always means a person is killed. The Giver explains to the boy how the people in the community do not understand the same sense of right and wrong that Jonas does. They follow orders mindlessly.
The Giver is the first one who mentions a plan. He wants Jonas to escape to Elsewhere. When Jonas leaves, the memories he has received will be released so that "the community has to bear the burdens themselves." The community will be forced to feel. They will have to deal with pain.
For weeks, The Giver helps Jonas prepare for his escape to Elsewhere. He gives Jonas "every memory of courage and strength." Jonas and The Giver make detailed plans. Jonas will leave in the midst of the busy Ceremony. The Giver will help him get food and supplies. They plan for The Giver to stay behind to help the people deal with the memories.
When Jonas goes home one evening, he finds out from his father that Gabriel is about to be released. Jonas is shocked. When everyone goes to sleep, Jonas takes Gabriel. He steals his father's bicycle and leftover food from nearby doorsteps. He flees.
Jonas had planned for the community to be busy and preoccupied by the Ceremony. In the original plan, the Giver was to save plenty of food for Jonas. He had also planned to give Jonas more memories to give him strength for his journey. Jonas had expected to travel alone, and not with baby Gabriel.
When Jonas leaves unexpectedly early, he does not have enough food. He does not have enough memories of courage. He has to calm and care for a baby. None of these factors had been in his original plan.
Basically, Jonas had to leave before he was ready and so he did not have all of his preparations made. He was also handicapped by having to take Gabe, but that was not really the same thing.
Jonas and the Giver had planned the whole escape out. First of all, they were going to have a few more weeks so Jonas could get more memories of strength and courage. Second, they had it planned so he would have a good head start before the people started looking for him. But then he had to leave before they had planned (because Gabe was going to get released) and Jonas did not have the courage he was supposed to have or the ability to leave just exactly according to their plan.