HSA with HDHC transitioning to LDHC

I (and many coworkers) currently have High Ded Plans with HSA though our company. When we turn 60 we will receive Tricare due to being Military Reservists. 

 

Can we still contribute while we are covered under the HD Plan? Once we transition to the low deductible Tricare can we use the $$ we contributed in the HSA prior to age 60?

 

Thanks