I always found it rather odd that older NPCs with craggy and wrinkly faces should have the neck of a 20 year old. So I experimented and added some definition to the necks of Cyrodiil. This is the result of said experiment.
This is pretty much my first attempt here, so things may not be perfect yet. I may update this in time, I may not. Time will tell.

What this mod does:

This mod alters the agemap normal maps from Nuska's Oblivion Character Overhaul v2 and adds extra detail around the neck and throat. There's some subtle blend toward the edge of the mesh to avoid accentuating the neck seam.

All human and elf males get new necks, older females also get new necks. Orcs, Kajiit and Argonians remain unaffected.

What this mod does NOT do:

Fix the neck seams. Ruin your game. End world hunger. Help you find true love. Make you a cup of tea.

Installation and requirements:

This mod requires Oblivion Character Overhaul v2 by nuska
which in turn requires Blockhead by shadeMe
which in turn requires Oblivion Script Extender (OBSE)
Once those are installed, simply extract Better Necks into your data folder and Bob's your Lobster!
A quick word of warning: this will overwrite some of OCO's files so make a back up before installing mine.

Special thanks to nuska for creating OCO. Tis a truly amazing work and you should be using it.