Complex sentence: He was born in Old Ross County in Watford in 1807 and in December 1825, at the age of 18 years, he enlisted in the British Army serving as a Private in the 18th Regiment.
Split into simpler sentences: He was born in Old Ross County in Watford in 1807. In December 1825, at the age of 18 years, he enlisted in the British Army, serving as a private in the 18th Regiment.