And thank you for not killing me for being Russian.
If you're anti-Putin that's enough for me :) And if you're interested in Poland and Polish culture then it's even better :))) I've come across some Russians who are wonderful people :)
Is 16 to old to learn Polish?
No, definitely not. I started learning English seriously only at highschool, when I was 15/16 years old. And it looks like you have a knack for learning languages :)
Do you know roughly how long it will take to become fluent?
I don't know, it depends how much time and effort you'll invest in learning. My guess is that, considering that you know Ukrainian already, if you study on regular basis then you should have some fairly decent grasp of the language after a year maybe? But once you have some Polish language basics from a language course I think that to become fluent it's important to immerse yourself in the language somehow - by watching Polish films, TV series, reading stuff in Polish and you could try to interact with Polish people on the internet, for example.
There are YouTube videos where people teach Polish, if not in Russian, then in Ukrainian. Ukrainians living in Poland also have YouTube channels in which they talk about studying Polish language, reality, culture, etc.
Here are some Polish basics lessons on YouTube in Russian:
I found a video of that guy from the first link giving advice on how to learn Polish fast (at first he talks a bit in Polish, but the rest of the video is in Russian):
Btw, I thought that this guy is Polish :O But he's from Belarus :O Wow, his Polish is perfect :O And he has no accent!
Btw, I forgot to add that if you're anti-Putin then you have nothing to worry about as far as Polish people in general are concerned. They will love you :))) Unless you're some kind of Stalin-loving communist, of course ;P