It has recently developed a new range of cheese that, at the end of the year end, requires a further 15 months to fully mature.

"the year end" is nearly exclusively used in the context of company finances or holiday times.

DThe directors of Mouse isare right.

The question indicates there's directors, not just one director, so should be consistent with that.

Because according to IAS 1 Standartd, any liabilityasset being avalilable in 12 months can be considered as current.

It doesn't make sense to talk about a liability being available, rather a liability would be due, as it's something you owe.

That's why, the cheese is not classified as current because they will not be ready for sale beyondwithin 12 months.

It's better to phrase this negatively because "will be ready for sale beyond 12 months" doesn't rule out the possiblity that's also ready for sale now.

They are called non-current liabilityassets.

Assets = things you own/possess
Liabilities = things you owe/are obliged to pay others

Case Study;:

It has recently developed a new rangtype of cheese that, at the year end, requires a further 15 months to fully mature.

The Directores of Mouse isare right.

Because according to IAS 1 Standartd, any liabilityasset being avaliable in 12 months can be considered as current.

The cheese is an asset, not a libility, since its being developed by the mouse company to be sold.

That's why, the cheese is not classified as a current asset - because they will not be ready for sale beyonduntil after 12 months.

They are calledIt is a non-current liabilityasset.

It (the cheese)

It has recently developed a new range of cheeses that, at the year end, will requires a further 15 months to fully mature.

(1) "Cheese" is generally uncountable. However, when we're talking about types/varieties of cheese, we will use the countable noun. This also applies to other nouns that are typically uncountable.
(2) "Year end" implies some time in the future, hence the future tense "will" is expected.

DThe directors of Mouse isare right.,

Bbecause according to IAS 1 Standart, any liability beingthat is avalilable in the following 12 months can beis considered as current.

(1) For formal writing, we tend to avoid starting a sentence with "because".
(2) "Standard" is already part of the abbreviation (International Accounting Standard).
(3) "Can be" implies that there is a choice or possibility. However, the IAS is a requirement, so no such choice exists.

That's why, the cheese is not classified as current because they will only be ready for sale beyondafter the 12 months period.

(1) The placement of the comma is awkward.
(2) I would suggest the addition of "only". "Only" emphasises the fact that the cheese will not be available before the 12 months are up.

They are calledonsidered a non-current liability.