How is a memory stored on a neuron or series of neurons?
And, given that, why would the amount of memory not be capped by number of neurons and synapses?
However, all of our current theoretical models on memory hold the premise that our capacity is infinite, as we are able to recall memories and information from decades prior (think about minuscule knowledges like walking). There is a "forgetting curve" model as well that supports the idea to spaced repetition as a method of reducing the latency of retrieving schemata from long term memory. Further, we identify diseases like Alzheimer's, dementia, etc as diseases as one of their trademark symptoms is the loss of mental ability. Is this forgetfulness due to losing scheme from long term memory or an inability to appropriately retrieve/process schemata?
Regardless, as I mentioned in my previous comment, if our capacity is infinite, then our only limitations are time and motivation. Adults, unlike children, need to be motivated beyond "because mommy and daddy said so" in order to allocate time to practice.
I think this is why "full immersion training" when learning a language is so powerful - regardless of motivation, you have allocated MUCH more time to "practice". Adults that move to another country and are willing to learn will have an easier time learning than someone that doesn't move but wants to learn or someone that does move but doesn't try to learn.
The last bit would be people willing to "teach" novice adults. This is another issue all together, but could still be framed as a time and motivation problem.
So perhaps there is in fact a limit, but you get a lot further with pointers than actually saving the periodic table, Hamlet, and a French dictionary.
We don't exactly know. Sweller's Cognitive Load "Theory". There's a reason it's a theory.