You can use as long as or so long as to say that one thing is true only if another thing is true. For example, if you say 'As long as you are under 16, you can take part in activities', you mean 'If you are under 16, you can take part in activities'.
You use a simple form after as long as and so long as.
You also use as long as to say that something lasts for a long period of time, or for as much time as possible.
Don't use 'so long as' in this way.
Be Careful!
Don't use 'as long as' when you are talking about distances. Don't say, for example, 'I followed him as long as the bridge'. You say 'I followed him as far as the bridge'.