Less old Shares are good.
But how can the miner reduce that himself?

Should not the miner just work and send all found shares to the pool? ... and the pool "decides" if the found share came too late?
Does the miner not send all shares to the pool, but decides after a self-invented logic whether he sends it or not?

Miner can only change pools and find one that matches his hashrate. I think it is mostly the pools fault.
I went from ethermine and 40 to 60 msec pings and tons of stales to anorak with 120 msec pings and no stales. Zero.