Schizophrenia makes it’s victims neglect and harm themselves. I believe this is the reason why overall having a case may or may not negatively impact an individual long term. Therefore, the negative impact related to age and the passage of time is secondary to the main issue of schizophrenia.
On the other hand, I know from first hand experience that individuals who had their first psychosis late in life, usually women of >50 years old, don’t recover at all until their death. Those who were born disabled also have it hard, in comparison to the majority of patients, who had their first psychosis in late teens to mid twenties. Those tend to get better with age.
The tendency may appear reassuring, however I personally met a 50-60 years old man who was deep in psychosis, and, inferring from his own words, he stayed that way since late teens.
Symptoms explicitly associated with schizophrenia tend to get better with age. But not overall health.