Shimano New 105 (black parallelogram arm on rear derailleur) was introduced in 1987 but was only 6 speed for its fist two years. It didn't get the 7 speed upgrade until 1989. In 1990, 105SC (silver parallelograms arm) was introduced. So, assuming it is OEM, if you've got New 105 with 7 speed, it should be a 1989 model.

The YDE60N certainly resembles the Peugeot model number format, with the exception of the Y prefix.The DE may designate a DEutschland specific model, which would make sense given the model name.