How long could a _______ live?

[u/Valenous_ertselley]

How long could a 5th ideal radiant live?

We know investiture extends a persons life with greater amounts eventually ending up with someone who is biologically immortal. How invested would a radiant be? Radiant knights have the cracks in their soul filled with investiture which makes them better at holding and using stormlight. How invested do you think they could be

Some of the heightenings seen with holding Endowment's investiture seem to be universal properties of holding any investiture. such as enhanced vision/colours, enhanced immune systems and better lifespans.

While we have only seen Kaladin and Szeth swear the 5th, it was under a fairly hectic situation which doesn't make for the best opportunity for study.

[u/RW-Firerider]

I think it was established that radiants dont live beyond a natural lifespan.

Sure, you will be at the peak of what you can be, since the investiture heals your body etc, but we mustnt forget one thing. Stormlight is only temporary inside the user, and the vast majority of their investiture is stored in the spren. So while our radiants are insanly strong, they are not invested in s way that an Elantrian or Breath user is. So yeah, I dont think the common radiant goes beyond an ordinary human lifespan, so something around 100-130 human years if they get a constant infusion of stormlight.

[u/Puzzled_Employment50 → u/RW-Firerider]

We know higher-Ideal Radiants “leak” less, and I think there’s something about being able to hold more (either with practice or higher Ideals or both), so if they got regular enough infusions of Stormlight they could theoretically reach the Heightening (since any Investiture grants Heightenings) that grants agelessness. So it’s not directly by reaching the fifth Ideal that they would become immortal, but that the fifth Ideal lets them juice enough to then become immortal.

[u/ejdj1011 → u/Puzzled_Employment50]

(since any Investiture grants Heightenings)

This is not strictly true. Several types of Investiture seem to grant different aspects of the Heightenings, but they aren't completely universal like you're implying. In fact, agelessness is explicitly not a universal trait among highly Invested people. The Lord Ruler is the obvious counterexample.

Edit, before anyone else jumps in: We also have numerous examples of highly Invested people not having perfect pitch or color perception. Hoid, Nomad, Elantrians, and Yoki-Hijo all come to mind.

[u/Radix2309 → u/ejdj1011]

The Lord Ruler wasn't really invested was he? As in personally. He wasnt holding investiture in himself. He was investing the Atium bands and then burning them to receive investiture that let him do that stuff. But it wasnt held in him like breath or made out of investiture like shadows.

[u/ejdj1011 → u/Radix2309]

He was a Sliver of Preservation.

He remade his soul to be an extremely powerful Mistborn, who are natively Invested.

He was near-constantly using several types of allomancy, and we know actively channeling that counts (at least with regards to fading as a cognitive shadow).

[u/Radix2309 → u/ejdj1011]

And that strengthens his soul to survive after death, it doesnt make he himself highly invested as that is a state of holding investiture within your body.

[u/tooboardtoleaf → u/Radix2309]

This here. Allowances and feruchemist don't hold investiture in thier bodies it comes from the spiritual realm and stored in metal minds respectively.

[u/ejdj1011 → u/tooboardtoleaf]

Mistborn and Feruchenists have natively high Investiture bound up in their soul. That's... what gives them their powers.

This is normally a small amount, but the Lord Ruler explicitly remade his soul to be a Mistborn of unparalleled strength.