Holy Cow!!
Ok, where to start. First and foremost,
you need more workers!!!!!!!
You have 13 cities and only 6 workers. Almost all your citizens are working unimproved tiles. With a Industrious civ I like
at least 1 worker per city. Germany is not Industrious. I would have at least 20 workers by now, probably more. Get mines on those shielded grassland (the ones with the gray mark in the middle of the tile) and have the worker road it before he moves to the next tile. Irrigate the wheat so the city grows faster. Granarys help here to. Roads=gold. Gold will let you research faster, as will library's. Thats why you are so far behind. You have no income. I mean 13 cities in 400 A.D. only bringing in 97 gold per turn is pretty sad. (No offense meant)
That's why you are only half way through the Ancient Age. All this goes back to not enough workers.
Take Nuremburg for example. City size of 4 and only 1 tile is improved (and it's only 'half' improved). All 4 citizens are working shielded grassland with no roads on them except one and no mines at all. By not having roads on those 3 tiles that are being worked, you're losing 6 gold per turn right there. By not having mines you're losing out on 4 shields which would get that temple built faster, which will keep them happy and working more tiles as it grows, which gives more gold............................etc.
Another example.....Hamburg.
Right now it's at size 6 and can't get any bigger until you build an aquaduct. Yet it's bringing in 6 extra food but only 2 shields total.
You need to get workers over there to mine that shielded grassland you irrigated and to mine the desert squares for shields. Don't forget to road the tiles too. Get a road on that forest square also so it is pulling in gold when you put someone working it. As you get this done adjust which tiles the citizens are working to get only 12 food but max shields so you can get that aquaduct built.
Building more workers ASAP and improving tiles will help tremendously. You also need a harbor somewhere so you can trade. You are going to need more than 1 luxury. Heck you could use it now.
Just some quick observations. I would be interested in seeing a save later on to see how you did.
