But if I am the generator of POS 100, I can also be the generator of POS 102 and the probability that I will be is a constant.
Like i said earlier, the current intention is that generating a block would consume the age of the output used to generate the block, so your age is reduced to 0.
But even if the age was not consumed, i don't follow how that would be a problem?
If i was a POW miner with 20% hashrate, i would constantly have a 20% chance to generate a block, no?
Not quite, unless you intend to award POS miners with a block reward? POW miners have a lot to lose by doing this, POS miners have nothing to lose.
No, rewards stay with POW miners.
It's simple really, if you don't mine a POS block, someone else will when the timestamp increments and their output gets lucky.