All a question of attitude, one should think. Actually it is a lot easier than that:
Small shirt collar on a slim fit shirt, small lapel on a tight fitting suit or jacket?
Then the narrow tie in 5,5 cm is your choice!
Normal collar on a regular fit shirt, classic lapel on a straight cut suit?
Then the wider tie in 7,5cm is right for you!
Age doesn’t matter at all, but body shape and size all the more.
From size 56 on, it is recommended to choose for the wider tie.