I work in maths research since the age of 17. At age 18 I lectured about my first paper at Sorbonne. I am currently a maths student at the University of Manchester.
A further note I want to add is that in maths and physics it is easy to read something and make yourself believe that you understood the concept when in fact you haven't. A good way to check for this bias that you can do on your own is to solve the problems in the book and check the solution afterwards.
On Quantum Information I (Mark) recommend Quantum Computation and Quantum Information by Nielsen and Chuang. It is not the newest book but it is better written than many other newer introductory books on the topic. https://www.amazon.com/Quantum-Computation-Information-10th-Anniversary/dp/1107002176
On Quantum Computation I recommend Quantum Computing Since Democritus by Scott Aaronson. https://www.amazon.com/Quantum-Computing-since-Democritus-Aaronson/dp/0521199565
A further note I want to add is that in maths and physics it is easy to read something and make yourself believe that you understood the concept when in fact you haven't. A good way to check for this bias that you can do on your own is to solve the problems in the book and check the solution afterwards.