I think the general issue is that while there is a focus on "ancient civilizations" (which, of course, covers India) Sikhism is too new to be covered in that. By the time the Middle Ages end and Enlightenment picks up almost all curricula swing back to Europe. I actually learned very little of what happened from 1500-1800ish around the world, besides how they related to the affairs of what was now some colony of a European country.
In the UK state education system it would be covered in Religious Education lessons, around ages 11-13. They cover most of the world's major religions. As a completely non-religious person I try to keep myself from telling my concientious son not to worry too much about his RE homework
And before (and optionally after). Also variously called Theology, Theology & Ethics, Religious Studies, Theology & Religious Studies, etc. - presumably because RE sounds like you're being educated to be religious, which is not the point at all.
