Ideally witnesses should not miss a block. Sometimes it is unavoidable due to server downtime etc, but factor in how many blocks they get on average - the top 20 get quite a few each day.

Last block is literally the last block number that they witnessed, block age is how long ago.

Reg fee is set by witnesses which when multiplied by 30 gives a price in steem for an account to be made. Many, including myself, have set it to 0.1 due to the higher price of Steem currently.

Ver. is software version. The latest is v0.19.2 and all witnesses should be running it.

Price feed pulls data from the exchanges for the price of Steem and feed age is how old that particular price feed was announced by that witness on the network.

APR sets any interest rate in your wallet.

Hope that helps.