I have Peter the younger born in 1731. I have his marriage to Susannah as Jan 18 1749 (when he would have been 18). I have his death as 1804 (when he would have been 73).
Your Jacob would have been born around 1783 (if he was 67 in 1850). That would have made Peter the younger age 52 when he had Jacob if he is the father of your Jacob.
The Jacob that I had was born in 1770 - he would have been 29 when his son Andrew was born. This would make Peter the younger age 39 when he had Jacob if he is the father of my Jacob.
Jacob remains my greatest challenge. I have our lineage up through Andrew for sure. And our connection with Peter and Peter and the Brethren is known as well. It is the gap between the younger Peter and Andrew (thought to be Jacob) that I am struggling with the most. I will post again if I learn any new info on Jacob.