At that age I was always watching them when they were not confned in any way. When they headed to the door,so did I - out we went. When they got alittle older they would sit at the door (could hold it alittle better). When I saw them at the door, I would ask - Do you want to go out? - over and over - I quess out of frustration with me for not opening the door and really having to go they would let out a little bark. That's when I would praise like crazy and open the door - out we went! After a while, if I wasn't looking they would let out a little bark.(they were taking to me - "I want to go out!"
With my Poppy I would take her to the door when I knew it was time to go and once outside I would say ' toilet' until she went. Then I would say good girl and give her a treat. She learnt that she had to go to the door to go outside.
Now as she gets older - I ask her ' toilet?' and she goes straight to the door. She sometimes also whines so I ask her again - and she goes to the door.
In general dogs bladders do not talk to their brains until they are 4 mths old - and I she is just that and I have defintely noticed her asking more to go out on her own.
A lot of toliet training is actually us reading their body language!