Peter Gideon was born on 22 March 1752 in Philadelphia County, Pennsylvania. 

He married Catherine, maiden name in dispute but possibly Ernst. He signed his Last Will and Testament in Loudoun County on 30 November 1835 and was proven in court on 14 March 1844. In the Will, he names his wife Catherine and his children Mary, Sarah, Elizabeth, William, George, and Henry. His obituary was published in the Leesburg Washingtonian and reads: 

"Departed this life, on the 15th (sic) of February 1844, near Hillsborough, Mr. Peter Gideon, in the 96th year of his age.  Mr. Gideon was a soldier of the Revolution, was at the Battle of Saratoga, and was also present in several other engagements, in all of which he sustained the character of a brave and dutiful soldier. He was universally esteemed by his acquaintances for his honesty and rectitude of life. The Weather at the time of his burial being very inclement, it was determined to defer until a more favorable season those marks of respect which in the opinion of his neighbors, the occasion demanded. Accordingly, on the 10th of June, a military procession consisting of the Cavalry under Captain Wright and the Rifle Company under Captain White, commanded by Col. Leslie, attended by the field officers and Regimental Staff, with the Hillsborough band of martial music, together with a very large number of citizens, moved in order from his late residence to Arnold Grove Church, where a very appropriate address was delivered by the Rev. Mr. Riley.
From a letter by Mark Gideon, a descendant:  "Dr. J.E. Copeland, of Round Hill, Virginia, a descendant of James Copeland, stated that James Copeland and Peter Gideon also served with Daniel Morgan's Riflemen and were great friends and lived as neighbors near Hillsboro, Virginia after the war. Dr. Copeland said that after the war, a barbeque was held on his grandfather's farm. There was a large crowd present. An ox was roasted and there was whiskey in abundance. Toasts were delivered by Peter Gideon and James Copeland, who were probably the only soldiers of the Revolution that were present.   
Peter Gideon's toast:
"Here's to the memory of Washington and his valiant band,
who forced the haughty red coats and drove them from our land.
The gallant lads of '76 we'll ever hear in mind, 
And I myself was one the them, which you will shortly find. 
My gun was heard at Trenton, aye, and at Princeton too, 
And many a haughty Red Coat my bullets have gone through. 
I did not fear King George's host of Cords and Commons, too, 
For some I made give up the ghost, upon my word, 'tis true." 

The Patriot died near Hillsboro, Loudoun County, Virginia on 5 February 1844.  

Sources:

1. Loudoun County [VA] Will Book 2b-2c 1841-1847.