It's been proven that there is life on other planets ever since we became self-aware. You're a few million years late.
Actually, you're a little bit early.
There's been speculation that there is/has been life on other planets for some time (not since the dawn of human consciousness, since back then people weren't even aware we were on a planet and that there were other planets), but there has never been any proof that there has been life on other planets.
There's information we've gathered which suggests, but never any proof. If there were actual proof, then we'd have actually discovered them.
As in, taken pictures or gone and met them or brought them back to us.
That is the only proof we could ever have that there is life on other planets/moons.