wow you just motivated me to make an account and get better at C++! Thanks!!
To develop an engine you need at first and only: Motivation
Without a game in mind which will use the game, you will lost your motivation very fast. Or why do you write it?
I myself started to develop an engine when I was 15 or 16... I had a game in mind... a big multiplayer first person shooter which was located in an open world. So I started... but don't find a good starting point... I really lost my motivation very fast. But this was not the end. After that I started to make an animation film... Again, I failed. Then I started a novel and understand that I really don't want to play or make a game.
I only wanted to tell a story. So I started my novel and continued to write it even today. I also continued my engine and it grew and grew... Today it is not finished, but this time my motivation is to make a game for my novel and to design huge software architectures. I really love design and this is the reason why my engine is alife even after 5 or 4 years.
What does that have to do with engine development?
Very much. Motivation is the most important basis you can have. But don't let it fly away. Fix it to something. I wrote myself a novel. What have you done?
Also buy books... many books... ten is not enough
Like Game Engine Architecture. Read all of them. Love them and of course understand them.
When you really only want to make a simple game you should use other available engines. Like Ogre, Irrlicht or maybe Unreal, Unity and if you really love high end, the CryEngine.
You have to invest a lot of time before you get something useful which you can call an engine. You will rewrite it many times. And everytime it will be easier. You will understand more and it will make you more fun. Of course there are also times where the motivation is down. Don't make you mad, you don't need pressure of time. I failed many times and I'm failing even today, but don't lost your motivation.
Maybe I've told a lot, but someday you will understand.
So at the end my suggestion to you:
Do it! Start your game engine development adventure!