The construction is idiomatic but it is not a set phrase and it is not limited only to durations (and not even to the past). Examples:
Meine Schulzeit ist schon ihre fünfzig Jahre her.
Der Mann wird schon seine vierzig Jahre alt sein.
Die Feier wird sicherlich ihre hundert Euro kosten.
Er läuft jede Woche so seine dreißig Kilometer.
Ihr Vorschlag wird bestimmt seine drei Jahre zur Umsetzung brauchen.
The seine/ihre references the subject of the sentence it is in. Compare the last example: Der Vorschlag means that we are dealing with masculine seine; it is not her because that would require feminine ihre. In your example sentence, the subject is das which is in turn a reference to das Lernen or das Englisch — but which one exactly is fuzzy and not necessary, we got the picture.
The expression as a whole is used to denote uncertainty. A good translation into French (I don’t know how well you speak that) would be […] cinquantaine d’ans […], […] quarantaine d’ans […], […] centaine d’euros […] and […] trentaine de kilomètres […]. (French doesn’t allow for an equivalent translation of the some three years; as far as I know the -aines are limited to steps of ten.)
It can be used more or less with anything where the number is followed by a ‘unit’ of some kind, even if the ‘unit’ is something like people or grains. But just giving a number does not work:
Mit zehn Würfeln wird er schon seine zwanzig wüfeln.
Mit zehn Würfeln wird er schon seine zwanzig Augen würfeln.
Of course, it does not work as well in the present tense since it’s usually clear what the extent of something present is, but it is not impossible. Usages in past of future tense are more common, though.
And finally concerning the usage, to the best of my knowledge this expression is used all across the German-speaking area in both written and spoken language.