@DannyHamilton  ,  the "niece"  was just a sample
anyway tnx for the additional info ...  expecially for last one  which I did not consider and  actually the only one that could  be an issue seeing that I cannot control it without a future intervention.
 

thank you !!   
that is  exactly what I was looking for . 

could you give me some example?? I googled a bit  but I was not able to find one software like that.

 

Hi,
I would like to know if there is a way to lock a wallet until a certain date or a block heigh will be reached.

For example  I would like to donate to my niece a wallet with some BTCs in but I would like she won't be able to open it before she's 18 years old.

Calculate block number to a certain time should not be an issue taking 10 mins as average time interval. But what about forcing the locked status?
To be feasible,  the method should avoid any future intervention by me so that she will be able to open it anyway even if I would be ( knock on wood ) RIP.

Any idea about ?

Tnx

  ...  now YOU are joking me ... I presumed was understood, anyway sure that mine was a joke, I cannot say the same about OP   


And what is supposed to mean  or prove a link to the blockchain? 

I am able to foresee Lotto numbers,   I could use them to win howmuch money I like so now I'm very rich and I don't even remember why I am still wasting  my precious time reading and writing posts on this forum;  

BUT  

I want to share my fortune with you and seeing that I am so needy and poor  I will ask you 0.33 BTC ....  

Yes it seems to me this have a sense and it  is fair.

COME ON            


  

Hi,  post is a bit outdated but someone else could find this info usefull anyway so ..

HAVE CARE!!! IF YOU LOOSE YOUR PRIVATE KEY ALL YOUR COINS WELL BE LOST

I start by saying that following are just my point of view and what I do to achive your goal.
I'm not sure this is the best nor the more elegant, but surely it works.

A wallet uses a private key and a public key (usually called "wallet address"). Basically public key it is used just to receive transactions and private to create and  send them, so that all are able to send coins to your wallet but none but you are able to send them: only you have the private key , only you are able to sign the transaction for sending coins from your wallet.
The public key  is derived from private one but it is impossible to do the reverse process, so you are free to give and expose your public key to receive coin from others with no fear,  because none will be able to retrive private key from it.

That said ,  worst thing you could do with a crypto currency  wallet is to expose your private key to public.
That is why last thing I would ever (IMHO) do is to trust a website asking it to provide me with a private key for my new wallet, especially if I want to store all my coins on that wallet and use it printed as "cold storage" .

I suggest you to generate a new wallet address simply using the original wallet software you want to use.
If you want to generate a keys couple on your own PC without having a complete wallet installation or want to have a particular pattern in you wallett  give a try to this vanitygen

If you don't like to download the whole blockchain  (as others above already suggested you) you have to use a lightweighted version of the wallet like "MultiBit" and/or "Electrum" bitcoin.
Googling for litecoin I found this electrum-lite  but I had no test on it.
   

Returning to the post topic, the easiest way I found to print my wallets and store them in a "secure drawer" is :

- send all my coins to a single public address (or wallet address)
- when transfer is complete, I copy that public address   and  :
   
   if GUI VERSION ...  goto  Help-> Debug> Console  ... and just type: 
   dumpprivkey LTCmyPubbddressgr4ZkpGtL5egY
   
        if CLI VERSION :
   litecoind dumpprivkey LTCmyPubbddressgr4ZkpGtL5egY

OUTPUT  (obviously these are all random  values,  not real pub/priv keys)

AGDFBKr4GZmLnoRwyBDMhAttsMxmjjAeG3Knh9cA89cbuA5cft8d
   

the output in both cases will be the corresponding private key of that public (wallet) address.
That is all I need to restore my wallett with all my coins in.

At this point  I can print it,  copy , produce a QRCODE (zint) and etc .... 

Remember anyone able to read that code will be able to open your wallet so you'd better put it  in a very secure place.
This is the reason I don't trust a website giving me my private key.


To restore it I just need to open another wallet of same coin . You can use an already in use or brand new wallet and  full version or
lightweighted one,   'cause the transactions are stored  into the block chain (and not in your single wallet) and then shared on the coin network. 

Well, I give the opposite command in the same way I got the private key:

importprivkey AGDFBKr4GZmLnoRwyBDMhAttsMxmjjAeG3Knh9cA89cbuA5cft8d   myrestoredwallet
 
(giving it a Label seems to be mandatory)

Restart of the wallet and here you are.

Before to do this operation on your real wallet and coins,  I heartily suggest you  to do some test with empty wallets or with coins with a very low BTC/$ value so that if you miss something in the process you won't loose all your coins at first attempt.

HAVE CARE !!!  IF YOU LOOSE YOUR PRIVATE KEY ALL YOUR COINS WILL BE LOST,
IF ANYONE IS ABLE TO READ YOUR PRIVATEKEY HE/SHE WILL BE ABLE TO OPEN YOUR WALLET
 ..... HAVE CARE AGAIN AND AGAIN


PS: I actually use to encrypt my private key with PGP before I print it 

It looks nice.
Good Job