Physical limits for a fixie rider
There are more factors involved. Gearing being a major one - it is much easier to skid on a 38x18 compared to a 50x14 which is more like a track ratio.
Other major factors include road surface, rider strength, dry/wet, tyre width, tread pattern, rubber compound and inflation.

Indeed, as others have mentioned additional weight might actually make it easier to skid given increased momentum and pedal resistance provided they shift their weight appropriately.

I would say there is no practical upper limit for rider weight but gearing and tyre characteristics (a really fat slick tyre with a big contact patch on dry tarmac) could prevent it. Nevertheless, skidding the rear wheel is an ineffective way to slow or stop your bike even if it is good fun.