You were asked to find answers to the following questions using Google Ngram Viewer
Do we tend to say 'I started' or 'I have started'?
Do English speakers say 'half a year' or 'six months'?
Do English speakers prefer to say 'recently' or 'lately'?
The answers are as follows:
I started is much more frequent that I've started or I have started. When talking about the past, we tend to use the verb 'start' in it's past simple form rather than the present perfect. This seems to make sense, starting something is the beginning of a process and the start is not connected to now. Having said that, it is possible to say 'I've started', For example 'I've started practicing the piano more often.' If the present perfect form (have + past participle) is used, it probably suggests that you started doing something recently.
German speakers often say 'half a year' whereas English speakers prefer to express this concept in months, that is 'six months'.
Google Ngrams will show you that 'recently' is more frequent than 'lately'. What it doesn't tell you, however, is that lately is a bit more difficult to use than recently. Read this blog post to find out why.