why i cannot see the sender of those 50BTC?
You can't identify a sender because there is no.
What you were looking at is a coinbase transaction (not related at all to the exchange called coinbase; they just used that term as a company name).
This is the mining reward. They assign themselve the current reward (earlier 50 btc, then halving every ~4 years; currently 12.5 btc).
This is the (only) way of generating bitcoins, mining them.
and last transaction from this address was 18-03-27 12:57:12 ... so someone spend 10 years without spending those bitcoin?
Yes. This is nothing unusual. Thereare quite a few possibilities why they didn't got moved yet.
He may:
- have forgotten about it
- have made a mistake and included an address without holding the private key
- have lost the private key (e.g. hard drive damaged)
- have a lot more btc's and those are a part of his 'holding stack'
- etc..