People’s ages in the Torah

From the perspective of Orthodox interpretations (Torah is G-d’s word), are the ages of people in Beresheet understood litetally? Does the Oral Torah explain how these ages are supposed to be understood and interpreted? There appears to be conflicts in the text–for example Terah was over 100 years old when Abraham was son but later Abraham believes its impossible for a 100 year old man to have children. Why would he think that if his own father did? [EDIT–TERAH WAS 70 WHEN HE HAD ABRAHAM.] But question remains, is there an explanation for why people had much longer lives until the time of Abraham?