All Heidenau racing tyres are DOT coded. You find the week of production and year of production on the side for example "3517" tells you week 35 of 2017. Also the tyre has a remark of the soft compound used ,mostly you will find the letters "DRY" On top of that a new tyre has a yellow line over the thread. Your tyre doesn't have all that ? Then you definitely bought a cheap road tyre ,forget all the seller tries to tell you.
You will also find a red paint dot on the side. Put that at the airvalve,please. The tyres has been examined for balance and if you mount it like that you will have the heavy side opposite to the valve.
Inside trick for mounting the 2.00-2.25-18: Take a sandpapering or grinding electric tool and round the sharp outer edge of the tyres heelsection. It will help a lot getting the tyre on a very narrow rim.