Is it possible to become a good Pianist if you're starting late?
Absolutely. Is this what you wanted to hear?
Ok first thing i want to clarify is that by "good" i do NOT mean as good as in concert pianist good before anyone says it...To be able to play fast and complex pieces...with relatively little effort.
When you say "to be able to play fast and complex pieces" and if you mean
actually play, you're probably playing as well as a concert pianist.

Complex is also extremely subjective.
I'm willing to put in the hours and effort needed but i'm just not sure if i am too old or not.
In all seriousness, I believe that anyone that isn't physically/mentally handicapped can obtain proficiency at piano playing, granted they have motivation. The question is, are you really willing to put up the hours and effort needed? I'd bet that the majority of people quit by the time they reach a level where they can actually assess the amount of work and effort needed to really play complex pieces.
Here's my advice:
If you really want to improve, focus on improving. A question like "Is it possible to become a good Pianist if you're starting late?" is debatable and a waste of your time.I can relate to you. I wasted years after getting a professional's (winner and runner up in a few international competitions) opinion that it was impossible for me to play well since I started too late so I quit and rarely touched the piano (this was my junior year of high school). About a year ago I started practicing the piano and made significant improvement (granted, the of amount I time I spend at the piano is sometimes ridiculous). I recently played for another professional (again, an international competition winner) and jokingly said I had aspirations to be a concert pianist, and he seemed to genuinely think I should go for it even after I revealed the lack of a repertoire (perhaps this was flattery?). I'm actually a very slow, undisciplined learner with terrible sight reading skills with my only redeeming musical ability being that I can play the sh*t out of small segments of a few "complex" pieces.
So, don't waste your time asking and contemplating useless questions like the title of this thread. Instead, ask questions like:
How can I do those leaps between those chords in 16ths in Petrushka 3rd movement? Do I need to slow my starting tempo to accommodate this portion of the piece?
Are my hands too small to even attempt this piece? If I roll these chords, will it make musical sense?
Is the way I'm practicing going to encourage the sound I want?