I think it would be useful mostly to those that as you said do the risky things It would be hard to judge how long you have left if you die alot

It could also be useful to others. For example, if I get an indication that I'll live longer than average, I might decide to appoint my grandson as heir instead of being forced to take over my middle-aged grandson when I finally pass away. On the other hand, if I shouldn't expect to grow too old, I don't need to worry about grandchildren when it comes to inheritance.

How about visiting a physician for an evaluation? The physician could estimate the character's lifespan predicated upon their remaining years having the same rate of lifespan-shortening events as the most recent user-specified number of years (default: since the player assumed control of the character).

This would give players some sense of how much time they have left with their current spark based on their history to date. It also allows estimates to account for changes in behavior. For example, a character who retired from soldiering ten years ago to become a blacksmith could project their future years based only on their past decade as a blacksmith.

I guess you´ll know. If he leaves his wife and kids and buys a new, fast ursaphant while he is an OPC, he is over the hill.

I might be wrong but i had understood that life expectancy and soul strength were two totally diferent things.

Your character can be at any point in his life but running out of soul strength.

our characters whatever their age when we take over have a soul strength of roughfly 50+ years,

What you're looking for is an indicator of your spirit strengh, it has less to do with your body and health, so with a physician than with your soul and as such a priest or shaman.

It could be translated by some dreams or nightmares when you reach half spirit strength

As Adam Kent said, your character's physical age will affect your available stats, so that's one way to tell. Looking at your character is another. Unless you're talking about available lifespan based on how many times you've died already, which is trickier because if you've died a lot, you're not going to see the end of a proper lifespan. But I'm not sure that can ever be given as a static amount. You could probably find someone with the rare rare magic powers and ask them if they can tell, but even that is a "If you stop getting CDG for the rest of your lifespan, you have this long left", but that number is subject to change if you continue to be CDG frequently. Better to simply evaluate how often you're dying and if that number is high, start preparing for the final kicker well before you think you need to. I do actually like that level of uncertainty though. It creates a tension around final death that probably helps some people to value the lives of their character just a little bit more.