Hello Aspirant!
You can start right from 11th by opting for science stream with math and physics.
With respect to a career in Astrophysics,
For an entry level job, you need to first complete B.Sc. in astronomy, astrophysics or physics. Following that you have to pursue M.Sc. in astrophysics, which is required for most research assistant and consulting positions. Lastly, to work with public - private sectors, science centers, or with colleges/ Universities as a researcher or teacher you must have a doctoral (Ph.D.) degree in astrophysics. This is a long career pathway and you might end up being 30 till you get there.
All the best.
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