This may be the best book for someone in their twenties and possibly in their thirties to read. I have been reading a lot of books on early retirement, financial independence, and self-improvement lately and The Simple Path to Wealth by JL Collins might be the most informative and motivating.
The book is based on notes, writings, and advice Jim had come up with for his then teenage daughter. It is about how to accumulate wealth by investing in index funds, but it is really more than that. It is a book about life and the opportunities that open up to you when you have the (FU) money to take risks and live the life you want.
Jim is a huge advocate of index funds and specifically Vanguard's because of their low fees. He suggests 100% stock portfolios. He does advise 85% stocks and 15% bonds for the weak-hearted. He isn't a fan of international funds.