What is max coin age ?
90 days
what is happend after this time with the coins ?
no automatic reorganisation ?
If I understand correctly, it just stops gaining interest at that point.
From my experience, blocks stop gaining weight after 90 days, but still get the interest past that. I staked some 97 day old blocks this month and got the extra interest for those 7 days. If you look at block 1542168 and do the math, you get a good example of why waiting for lowest diff and adding your interest is better than compounding at a higher diff.