You should keep your kitten indoors for as long as you can and, ideally, for at least four months. After that, the best approach depends on your local environment and your cat’s temperament: some Burmese are very happy as indoor cats but some are not and you need to strike a balance between giving your cat the level of freedom it desires and your own peace of mind.
It is advisable to ensure that your cat is always indoors before dark because there are many night time hazards: foxes, badgers and feral cats, cars and people who steal cats.
It would be foolish to let a kitten out if you live on a busy road but if you live in the country or a quiet suburb it shouldn’t be a problem. Remember that because of the inquisitive nature of Burmese your cat will always want to see what’s on the other side of the road.
There are several intermediate steps between the cat being kept indoors and being given complete freedom. You can build a run in the garden or install a cat proof wire fence. Much more information is available from, for example, International Cat Care.