It depends on the miners.
However, today it’s not profitable for average persons to mine Bitcoins. Now only specialized companies and pools can generate profits.
AntPool is the largest Bitcoin miner as of now. It is operated by Bitmain, a Chinese company that develops ASIC devices (special mining machines). Their machines are the best in the world, and the company says that over half of the miners worldwide use their equipment.
If we don’t count the revenue from their machines and other products, then Bitmain can generate from $70 to $100 million annually from mining alone.
Thus, we don’t speak about billionaires anyway – there is no billionaire entity that has grown from mining to this point. Bitmain is the largest miner in the world, and it needs at least 10 years to generate $1 billion from mining, but this is only considering the current conditions, because as time passes, mining becomes even more challenging, as the reward per block is lowered.
Here are the largest miners as of today:
As you can see, the five largest miners have 70% of the mining market, and none of them can reach $1 billion only from mining.
You can profit from mining by becoming part of a mining pool. A mining pool is a group of miners who join together to make the process more efficient and have the chance against competitors. The profits are then shared among the pool members. However, you need an initial investment of course.
The mining process requires much electricity, which is why guys who have this can succeed:
Otherwise, starting alone is not that profitable.