Samson age is never mentioned in the bible but we have this;
30 And Samson said, Let me die with the Philistines. And he bowed
himself with all his might; and the house fell upon the lords, and
upon all the people that were therein. So the dead which he slew at
his death were more than they which he slew in his life.
31 Then his brethren and all the house of his father came down, and
took him, and brought him up, and buried him between Zorah and Eshtaol
in the buryingplace of Manoah his father. And he judged Israel twenty
years. (Judges 16:30-31 KJV)
A Biblical judge was a ruler, military leader, and someone who presided over legal hearings
So were all those that were numbered of the children of Israel, by the
house of their fathers, from twenty years old and upward, all that
were able to go forth to war in Israel; (Numbers 1:45 KJV)
So by this Samson become a judge at the age of 20 which is in chapter 14:4 when God start to use Samson as a judge to confront the Philistines and died at an age of 40 years old.
(His parents did not know that this was from the Lord, who was seeking an occasion to confront the Philistines; for at that time they were ruling over Israel.) (Jdg 14:4 NIV)
The Philistine woman in Timnah
In Judges chapter 15 vers 2 the word used by the father is קָטָן qāṭān and does not give a specific age. It means young, little, small.
And her father said, I verily thought that thou hadst utterly hated her; therefore I gave her to thy companion: is not her younger (H6996) sister fairer than she? take her, I pray thee, instead of her.
The same word קָטָן qāṭān is used for Benjamin;
And we said unto my lord, We have a father, an old man, and a child of
his old age, a little one; and his brother is dead, and he alone is
left of his mother, and his father loveth him. (Gen 44:20 KJV)
Benjamin was born before Joseph was sold into slavery. Actually, he was birthed by Rachel when Jacob and his family were returning back home from Laban, his father-in-law (Gen 35:18) and Joseph was 17 when he was sold into slavery, and 39 when they came to him in Egypt. So if Benjamin was 1 year old then he was 23 years when his brothers referred to him as קָטָן qāṭān