The universe is 13-20 billion years old depending on who you ask.
Earth has been here 5 billion.
That gives us 8-15 billion years of missing time.
Within 100 to 200 years mainstream science will know how to get to the stars so consider a race 1000 years ahead of us, or 1 million years ahead. It would be probably impossible for them to miss us since we probably stand out like a sore thumb.
Here, this the most comphrehensive presentation that I have found on it.
