Where is extraterrestrial?

One day in 1950, Nobel laureate, physicist Enrico Fermi and the other 3 physicists lunched at the dinner table, Fermi suddenly said one sentence: "where are they? "Other people quickly realized that Fermi was still pondering what they just argued about the spacecraft and alien. Later, Fermi's words became the famous "Fermi Paradox".
"Fermi paradox" is connotative of this meaning: In theory, humans can use 100 million years of time to fly to every planet of the galaxy, then the aliens as long as their evolution is 100 million years earlier than humans, they should now come to the Earth. Why do they not come? Where is their precise whereabouts?
The reason that this paradox has persuasion is because it is based on two facts of Milky Way galaxy: First, the Milky Way galaxy is very old, about 100 million years of age; second, the diameter of the Milky Way galaxy is only about 10 million light-years. Therefore, even if the alien is only traveling in space in the speed of one-thousandth of the speed of light, they can only take about one million years across the universe - this time is far shorter than the age of the universe. If aliens really exist, then they should arrive very earlier.