When I try to enable SSH on my router, got the "Please create RSA keys to enable SSH."

So here we are :

rtr-l3(config)#conf t

rtr-l3(config)#aaa new-model
rtr-l3(config)#username admin password 0 a2m1
rtr-l3(config)#ip domain-name ssh
rtr-l3(config)#crypto key generate rsa
The name for the keys will be: rtr-l3.ssh
Choose the size of the key modulus in the range of 360 to 2048 for your
  General Purpose Keys. Choosing a key modulus greater than 512 may take
  a few minutes.

How many bits in the modulus [512]: 1024
% Generating 1024 bit RSA keys ...[OK]

rtr-l3(config)#crypto key generate rsa general-keys label ssh-key
rtr-l3(config)#ip ssh rsa keypair-name ssh-key


Update :

You can run the command "auto secure ssh"