I would restate that as "We know that there will be lower real rates in the future, and the reason we know that is because of the changes in the demography."
If this next part that I write is difficult to understand (because it may be for someone still learning English and I don't know your background), don't worry too much about it. :D
The word "imply" has to do with either causation or logical reasoning, depending on the context.
Causation: If A implies B, then A causes B. Holding a ball in the air and letting go implies that the ball fell to the ground.
Logical reasoning: If A implies B, then B must be true if A is true. If it is raining, this implies there are clouds in the sky. The rain doesn't cause the clouds to be there, but we know that the clouds would have to be for it to be raining. The presence of rain implies the presence of clouds.
I hope that's helpful.