bitcoin back-end blockchain storage bitcoin uses blockchain
so blockchain is peer to peer, 
every peer stores the data

so I wonder where does the data of all the bitcoins is stored?
who is peer in case of bitcoin?
so that peer gets data related to bitcoins all over the world?

as the bitcoins grow isnt it becomes slower and slower to retrieve information?
Each non-pruning full node (peer) stores a complete copy of the blockchain - pruned nodes store a complete copy of the current state, but may not have all historical blocks available.

When a node validates a transaction or a block, it is only validating it against its local view of the blockchain - this means that looking up data is pretty fast, since all of it is available locally.

As the blockchain grows, access time for most data still remains mostly the same due to the nature of the key-value store used by bitcoind - look up times for a key value store are roughly constant, although data that is cached in memory can naturally be accessed faster.