It is nearly impossible to keep balancing date on all speeds and difficulty levels so the modders won't waste time on it. The date is meaningless so just ignore it.
Also, in real life, after the end of the ice age, 12000 years ago, the sea level has risen 120 meters, often in pulses (tsunamis), causing many deaths and much destruction, often swallowing whole cities into the sea, and since most humans tend to live near the coast, this has set back the development of human economy probably by thousands of years. Underwater archeologists have found several large very old stone cities deep under water off the coast of Asia. This is not (yet) implemented in this mod.
Flooded kingdoms of the Ice Age:
https://www.youtube.com/watch?v=Va0BIqfzpvo
If you are behind on making buildings, it tells me that you probably want to build every building available in every city. If you are instead more selective, the building availability is ok, especially on higher difficulty levels, where tech is slower and it takes longer for new building options to appear.
By the way, changing game speed changes both the tech speed and the building cost, so it won't solve your problem of too many buildoptions. But a higher difficulty level will. A slower game speed basically gives you more unit moves compared to your economic and tech production.