Time in our Universe versus time in Black Holes The universe is immense and 13.8 Billion years has passed overall since it was formed in the Big Bang event.
If time greatly slows down inside a Black Hole (BH), then logically very much less than 13.8 Billion years has elapsed inside any BH that has formed since the Big Bang, in our universe.
Thus, inside a BH, has any matter had sufficient time inside the BH to transit from the event horizon to the center ?
I understand that time for the in-falling matter seems normal, but that doesn't mean it is unlimited.  There is still the matter of the limited 13.8 Billion years in normal time outside the BH.   Any slower time means less than 13.8 Billion years has elapsed inside the BH.
Maybe the age inside a BH is only a few seconds total elapsed time!
From inside the BH's perspective, matter must be falling in at an infinitely fast rate and piling up into a very condensed shell at the event horizon!
IF that is true, then would not the BH be just a huge condensed matter shell only a few meters thick without any central singularity formed - in 13.8 Billion years viewed from our perspective outside ?
 A: The most important feature of a black hole is the cosmic censorship, that means that the event horizon is a sort of screen which is entirely intransparent for our scientific methods. For this reason, the interior Schwarzschild is not corroborated by any experimental insight.
A black hole may not be imagined as a sophisticated world, in fact, according to our knowledge it has very little features – mass, position, diameter of event horizon, angular momentum, and - possibly - some Hawking radiation.
The existence of black holes may be observed, and by this we may assign an age to each black hole. In contrast, there is no information about the existence of some proper time of some hypothetical observer inside the black hole. All the contrary, we must admit that spacetime of general relativity ends at the event horizon of a black hole, and so does our definition of time.
A: It is a misconception that mass creates time dilation, in reality it is stress energy, and the difference between the strength of stress energy of the black hole, and the rest of the universe (let's assume empty space).
Now you are correct that because of this difference in stress-energy, that causes time dilation, clocks at the black hole will seem to tick slower relative to clocks in empty space.
Now you are saying that you understand that infalling clocks and observers would seem their own clock to tick normally. It is only when they would compare it to clocks outside that they would see their own clock inside the hole ticks slowly.
But you say it cannot be unlimited. Now in reality, 13.8 billion years might seem a long time to us, but it might be just a second in the frame of an infalling observer in a black hole.
To clarify, there were no black holes 13.8 billion years ago, but let's disregard that and say that there was a black hole so long ago. Let's assume an infalling observer looked at his clock inside the hole at that point (again, assuming this would be already existed 13.8 billion years ago), and compared it with clocks outside the hole.
What he infalling observer would see, on his own clock, is that it ticks normally just 1 sec in this example, but if he compared it to clock outside the hole, those clocks ticked 13.8billion years already and here we are. 
So 1 sec in the black hole might easily be 13.8 billion years outside the hole. So no, it is not neccesseraly true that all that matter that falls into the black hole would have reached the singularity by now (13.8 billion years later on an outside clock).
It is because 13.8billion years on an outside clock, might just be 1 sec inside the hole. In reality, we do not know if anything ever reached a singularity inside any black hole ever (that is any new matter infalling from outside the already formed black hole).
A: 'Has any matter had sufficient time inside the BH to transit from the event horizon to the centre?'
One can regard the black hole and its contents as isolated from the rest of the universe, in that no information can be transferred (as of 18th May 2019!) from the black hole to the universe. In this sense the matter inside the black hole has had as long as the age of the black hole to progress to the 'singularity'. 
Relative to our time, yes, the matter in the black hole has experienced a very small amount of time (much much smaller than the age of the black hole). The matter does fall in at a finite rate all the way up to the singularity. 
