i have a four month old german shephard and have been given conflicting advice on how long i should walk him does anyone have any advice

The rule of thumb is 5 minutes per month of life so that would be no more than 20 minutes for a 4 month old.

And that literally means 10 minutes each way.

If you are trying to get to grips with lead training and heel work (are you going to class?) then it's just as effective to practise these in the garden and round the house.  Limit your walks to the concept of 'let's go and see/experience something new today' and he'll get more benefit from the outing.  Driving to new destinations is good too so that he can see more things but without having to cover the distance himself.  Proper walking just for the sake of exercise can be left til he is older.

It's a good age - have fun :)

I find a good rule of thumb is 1 minute per week of life....10 weeks 10 mins...20 weeks 20 mins...easy peasy!!!...by 52 weeks (1 year) you can drop it and do what you like.
Aileen