There are several saints named Cyriacus so you need to be more specific.
If you are referring to St. Cyriacus of Iconium, the child martyr and son of St. Julitta, he was born about the year 301 AD.
Cyriacus was born in 2##.
Cyriacus Spangenberg was born in 1528.
Cyriacus the Anchorite was born in 448.
Cyriacus died in 303.
Cyriacus Spangenberg died in 1604.
Cyriacus of Jerusalem died in 133.
Judas Cyriacus died in 360.
Cyriacus the Anchorite died in 557.
Julitta, also known as Julietta, mother of St. Cyriacus, is the patron saint of:death of childrensingle laywomentorture victimswidows
There are many saints who died as children. Here are a few: St. Philomena, St. Cyriacus, St. Maria Goretti, Saint Agnes, St. Dominic Savio, St. John Berchmans. Also we can not forget the Holy Innocents who died when Herod ordered all the children of Bethlehem killed. There are also several Blesseds who died as children: Bl. Jose Luis Sanchez, Bl. Francesco Marto and Bl. Jacinta Marto
No, there have been a number of saints younger than Agnes. The first were the Holy Innocents who were murdered by King Herod soon after the birth of Christ. Other young saints include St. Cyriacus who was martyred at the age of 5 or 6 and St. Maria Goretti who was murdered at the age of 11.