Mathematicians ahead of their time? It is said that in every field there’s that person who was years ahead of their time. For instance, Paul Morphy (born 1837) is said to have retired from chess because he found no one to match his technique that very much resembled modern chess theory.
So, who was the Paul Morphy of mathematics?
My top vote would be for Ramanujan.  With severely limited resources, he was able to formulate deep number-theoretic identities that the top mathematicians in the field at the time hadn't the imagination to conceive, let alone the slightest clue to prove.  A close second would be Evariste Galois--dead at the age of 20, he had already established the foundations of what is now an entire algebraic theory named after him.  The world will never know what mathematics he could have discovered had he lived.
You can have people 'ahead of their time'.  What really happens is you have 'mainstream maths', and than a whole lot of eccentrics who are 'doing their thing', which may or may not be where maths will be in 20 or 30 years time.

There are several things one has to note here.  Some of us are just not really good at sitting down and writing theorms and proofs etc.  I have a degree in physics, which means you approach the world in a different way to what the mathematicians do.  None the same, you can do 'real maths', but do it without having to prove the tedia involved.

The sorts of things i needed for my studies in weights and measures, and number-bases (i use base 120 natively), etc, i had to go back something like 100 years and look at what the eccentrics were doing.

So, really, people really can be 20 or 30 years ahead of the mathematics, you just got to be in the right crowd of eccentrics.