Could the size of something determine its experience of time? For instance, if our planet was 50 times bigger, would time elapse differently given the gravitational difference?

Yes, but you need to be near the extremes before you start noticing a difference from the outside world.

Your statement of 50 times bigger is too imprecise for this question.

At 50 times the mass. you would scientific equipment to tell the difference, but you likely would never know.

At 50 times the diameter, we are in small star territory. We are still talking about insignificant changes.

At 50 times the mass, but the same diameter. Things are starting to get interesting but still wouldn’t get to a 1% difference with everything else remaining the same.

At 50 times the mass and a diameter of a grain of sand. Now we’re talking, but you’d still need to get within a foot of thing (I’m approximating, as I’m too lazy at the moment to work out the actual distance.) Should you decide to get within a foot of that thing you should notice a decent level of change, but you’d probably be too busy dying horribly to take note as it ripped chunks off of you.