I'm sure we've all been in this situation: you are meeting someone for the first time and want to find out something more about them. It could be at a networking event, they could be a new colleague or someone visiting from another company location.
Once we have found out some initial information we might want to ask them how long they have:
run their own company
worked for the same organisation as you
or, played the piano
To ask these questions we use the present perfect tense (how long have you...?).
This is because the person we are talking to is still carrying out the activity we are asking about: they are still running their own company, working for the same organisation as you, or still playing the piano.
How long have you been running your own company? I have been running my own
(not 'how long are you running your own company?') company for ten years.
(not 'I run my own company
for ten years')
How long have you worked for the X organisation? I have worked for the X
(not 'how long are you working for the X organisation?') organisation since 2007.
(not 'I work for the X
How long have you been playing the piano? I have been playing the piano
(not 'how long are you playing the piano?') for 3 years.
(not 'I play the piano for 3