A lot of points here I find plausible. On the changing habitability of the universe, Earth has quite a lot of heavy elements. Those are, as I understand it, generally thought to be formed by supernovas, and so they should be rarer the further back you go in the history of the universe, as the earlier you go, the fewer supernovas there would have been so far. Some of the heavy elements are definitely involved in life (indeed, though I was mostly thinking of further up the periodic table, carbon and oxygen are relatively heavy compared to the majority of the matter in the universe, and not produced in any quantity by the normal activity of young stars, though they don’t require supernovas). Further, just having enough heavier elements around may be important in planet formation.
Of course, this is all quite speculative. Perhaps some substantial amount of heavy elements was produced in the big bang. And very big stars have very short life cycles, so if there were a lot of very big stars when the universe was young, there might have been a lot of supernovas very early on. Or there might be other ways for heavy elements to form. But obviously if none of these were the case, and so heavy elements were much rarer in the early universe, that may mean that there are unlikely to be many star systems with remotely earthlike planets that are older than our solar system.
A lot of points here I find plausible. On the changing habitability of the universe, Earth has quite a lot of heavy elements. Those are, as I understand it, generally thought to be formed by supernovas, and so they should be rarer the further back you go in the history of the universe, as the earlier you go, the fewer supernovas there would have been so far. Some of the heavy elements are definitely involved in life (indeed, though I was mostly thinking of further up the periodic table, carbon and oxygen are relatively heavy compared to the majority of the matter in the universe, and not produced in any quantity by the normal activity of young stars, though they don’t require supernovas). Further, just having enough heavier elements around may be important in planet formation.
Of course, this is all quite speculative. Perhaps some substantial amount of heavy elements was produced in the big bang. And very big stars have very short life cycles, so if there were a lot of very big stars when the universe was young, there might have been a lot of supernovas very early on. Or there might be other ways for heavy elements to form. But obviously if none of these were the case, and so heavy elements were much rarer in the early universe, that may mean that there are unlikely to be many star systems with remotely earthlike planets that are older than our solar system.