In Bitcoin, some block heights are required for spending coinbase transaction. But in Ethereum, there's no input/output. Then, is there any maturity time for using block rewards in Ethereum? If yes, how it works?
No there are not delays. Indeed all accounts have an explicit balance and they can spend the money they have. Obviously, it is possible that, before block
x I have 0 money in my account, then I succefully create my block and receive a reward. From block
x+1 I can spend the money because my balance is no longer 0.
N.B. it is possible that the fork of the blockchain in which I had money and spent it will be deleted (because other forks are accepted as canonical), but potentially, once you have money you can spend them. Blocks are considered really confirmed after some time (in Bitcoin 6 blocks, in Ethereum 12, as stated here.