Yeah but Gridcoin isnt Proof of Stake, its Proof of Research.  The PoS is combined with the BOINC work which changes the way it works, staking a block isnt purely based on the coin age.

I get much more reward from my BOINC contribution in each block than from the PoS interest, so there is no barrier to me overtaking a larger coin holder if I exceed their BOINC contribution.  The last block I got 3-1 BOINC versus PoS.