A 90kg person can definitely get to it in 60 days. My only fitness before starting BJJ in 2015 was running (which I did regularly) and I weighed about 90kg. I was successfully hand walking down the length of the mats during our warmups in a couple months (though I was falling a lot in the first month, and was never stellar at it).
I'm also uncertain how 50kg is the weight of a normal person. If I get below 75kg I'm around 5% body fat, and I'm barely above the US male average height. Getting to 50kg would mean losing a substantial amount of muscle mass, I literally have never had enough fat and so little muscle (even when I was obese) to be able to healthily cut down to that weight. And, again, I'm only about 1cm over the US average.