Student or Learner
Why not erring is human or making mistakes is human?
"To err is human, to forgive is divine." is a quote form my favorite English poet, Alexander Pope (1688-1744).
It is acceptable (although somewhat old-fashioned) to use an infinitive instead of a gerund as a subject.
To swim is an enjoyable activity. infinitive
Swimming is an enjoyable activity. gerund
You said itīs acceptable... Do natives use sentences like this, in everyday English? Like To live in Rio is not as safe as it used to be...?
In my dialect of English, it is much more common for people to say:
Living in Rio is not as safe as it used to be.
It is not as safe to live in Rio as it used to be.
"To live in Rio is not as safe as it used to be," would be universally understood, but it would sound unusual and unnatural.