for me the real passive income is saving your money, you save your money now, you can save $100-$500/month then use your saving for passive income in your day of retirement 
The time when you get into your retirement day, the value of your money will be 10 % less atleast. Assuming that the inflation rate is on average of 5 % per year and if you save for 25 years until your retirement day then you could be able to do the calculation of your own on how less valuable your money will be at that time so saving is definitely not your best bet to retire