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 8 cm 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.