The present perfect seems the only possible tense here. The other possibility is to rejig the sentence as: I am an English teacher and have been for about ten years now …
Thanks a lot for your quick response and your clear explanation. I came across that sentence on Myngle.com – a language learning community. Have you heard about that website?
Regards,
Torsten
PS: The verb rejig was new to me too, thanks for teaching it. Even my Babylon Translator does not have it![YSaerTTEW443543]
I would take this structure (“I am…for/since” instead of “I have been…for/since”) as a first language indicator. Thus e.g.
J’attends depuis longtemps
may be rendered by a French native speaker as
I am waiting for a long time
instead of
I have been waiting for a long time
(The same mistake, curiously, is sometimes made by English natives, when translating from languages which use the present instead of the present perfect in such cases.)