For those who may be wondering about experience levels in the back end of the defense, they've only increased each year in 2016 and 2017, and (potentially) again for 2018.
Previous NFL experience:
2016 Cornerback = 4150 snaps
2016 Safety = 8600 snaps
2016 TOTAL = 12,750 snaps
2017 Cornerback = 8100 snaps (Gilmore added, Ryan subtracted)
2017 Safety = 11,150 (just in 2016 experience added to the existing roster)
2017 TOTAL = 19,250
2018 Cornerback, potentially = 12,000 (J-Mac added, Butler subtracted)
2018 Safety, potentially = 14,100
2018 TOTAL = 26,000 snaps of previous NFL experience
It seems reasonable to guess that this is among the most experienced secondaries in the league.
The trick now is how to maintain a high experience level and avoid an "experience crash landing" in the near future like what the Front-7 went through in 2017. With Chung and the McCourty brothers turning 31 in Camp, and with D-Mac's extremely high cap hits for 2018 & 2019, and with only Gilmore, Cy Jones and the rookies signed beyond the end of this season, that may be more difficult than it seems right now.