The One Ring and invisibility

[William Cloud Hicklin]

The Ring also confers unnaturally long life to the mortal wearer, I wonder if this is also just a side effect rather than an intended power.

No, I don't think so. It was quite deliberate, indeed the principal function of the Rings. Celebrimbor's purpose was to slow or halt the ravages of the swift passage of Time in Middle-earth; to allow the creation of places like Lorien wherein the Elves would feel the burden of years the less. I suppose one could say that it was 'unintended' in the sense that he never intended for Mortals to have them, of course- for them serial longevity was unnatural and eventually a horror.

I suppose just keeping the Ring in your pocket or on a chain would not confer long life. Gollum, I suppose, probably wore the ring for very long periods when living under the Misty Mountains. He probably wore it while sleeping.

This isn't so, in fact it's expressly refuted in the text. Gollum wore It very little in the dark tunnels. Bilbo put it on occasionally, and briefly. It was possesion which caused the 'preservation,' and can be seen in Frodo's case as well even though he never wore it before his quest. Bilbo was already aging at the time of the Council: possession had passed on 17 years hence. But of course the really rapid aging only took hold when the Ring and all its works were nullified.

Had Bilbo or especially Gollum worn the Ring for extended periods they would have become wraiths.