Clones have accelerated aging.

Eh I’ll chalk this up to poor Lucasfilm planning, I remember initially his son in Canon wasn’t a clone. But it can be easily retconned by saying that the clone had accelerated aging.

Why would Palpatine’s clone not look like his younger self and why would a clone he presumably wanted to possess to extend his live intentionally have accelerated aging is beyond me.

Yeah it's a wierd decision to make especially since something like excelerated aging would be decided before the clone would show any signs of force sensitivity.

I honestly would suggest you to wait until the novel Shadow of the Sith is out, in which Rey’s parents will be featured with more detail, and it may finally give us confirmation about his “birth year”. Until its release, that information will probably change a lot.

Some Cloners choose to imprint their clones DNA with accelerated ageing. So it in actual years could be possible, That is actually viable as all he wanted with his "children" was a dynasty not a family.

The birth date is correct and sourced. He probably was “born” full-grown, like Snoke or Palpatine’s reborn body.