As with most things, this depends on the individual. If your child has been invited to take advanced coursework, (usually called a gifted and talented program) the academic details may begin in junior high school. Academically advanced students can usually take classes for high school credit in junior high. Algebra and Spanish are usually some of the first offerings.
With non-academic preparations, the age can be much younger. Just like you must teach your child to share with siblings or playmates, you will need to teach them the importance of sharing by giving back, otherwise known as volunteering and community service. This kind of behavior is best taught by example. Involving small children in your volunteer efforts will teach them the importance of these activities without you having to say a word. If they don’t develop a love for the community service you have chosen to do, help them to find something that touches their heart.
Introducing ideas to small children that will become important life skills allows these things to become a part of who they are. The alternative is to raise feral children and attempt to civilize them during the most rebellious phase of their development. A parent is a superhero in the mind of a small child. Use that influence before they enter that know-it-all stage when everything you say is stupid. They will remember and hopefully use those early lessons you taught them before they go through puberty and become an authority on everything.