Ruling on renting for an indefinite period; and what is the maximum length for renting?

One of the conditions of a rental being valid is that it
should be for a definite period, such as one or two years. If it is
indefinite, such as saying, “I will rent out my house or my shop to you for
as long as you live” and so on, the rental contract is not valid. 

Ibn Qudaamah (may Allah have mercy on him) said: If rental is
for a period of time, then it must be definite, such as a month or a year.
There is no scholarly difference of opinion concerning that as far as we
know, because the period is the guideline for the contract, so it must be
known.

End quote from al-Mughni, 5/251 

Secondly: 

There is no maximum limit for a rental contract for renting
out of specific property. The rental contract is valid for however long the
stated period lasts, but that is subject to the condition that it is thought
most likely that the place rented will continue to exist. 

Ibn Qudaamah (may Allah have mercy on him) said:

There is no maximum period for rental; rather it is
permissible to rent out a property for as long as it will continue to exist,
even if that is a long time. This is the view of all scholars, except that
the companions of ash-Shaafa‘i differed concerning his view, and some of
them said that he had two opinions, one of which is like the view of all of
the scholars, and this is the correct view. 

The second view is that it is not permissible for longer than
one year, because there may not be any need for more than that. 

Some of the scholars said that he had a third view, which is
that it is not permissible for more than thirty years, because usually
properties do not last for more than that, and prices and rents change. 

Allah, may He be exalted, tells us that Shu‘ayb (peace be
upon him) said: “…
on condition that you hire yourself to me for (the term of) eight years.
Then if you complete ten it will be of your own accord” [al-Qasas
28:27].

And what was prescribed for those who came before us is also
prescribed for us, so long as there is no evidence to show that it has been
abrogated. 

If a contract may be valid for one year, it is may also be
valid for longer than that, such as contracts of buying and selling,
marriage, and sharecropping. There is no evidence to suggest that it should
be limited to only one year or thirty years, or less than that, or more than
that.

End quote from al-Mughni, 5/253 

It says in Zaad al-Mustaqni‘: If a person rents a
house and the like for a certain period, even if it is for a long time, and
it is thought most likely that the property will continue to exist during
that time, then it is valid. 

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
Whether it is thought that the people who are party to this contract will
still be live or not, such as if he rents out this house for a period of
sixty years, then the rental is valid, because it is thought most likely
that the house will continue to exist for sixty years, especially if it is
made of concrete and is new. So if it is most likely that it will continue
to exist, then renting it for this period is valid. However, if it collapses
before the end of that period, then the rental contract is nullified,
because the property the contract refers to has been destroyed, and the
renter is entitled to compensation for the period he paid for but did not
complete. 

The words “if a person rents a house and the like for a
certain period, even if it is for a long time, and it is thought most likely
that the property will continue to exist during that time” mean that if he
rents it out for a long time but thinks it most likely that it will not
continue to exist during that time, then the apparent meaning of the
author’s words is that the rental contract is not valid. … If he rents a
camel to him for a period of fifty years, then it is not valid, because
camels do not live for fifty years; or if he rents a car to him for one
hundred years, it is not valid, because cars do not usually last that long,
unless he does not use it at all, which is another matter altogether; but if
he does use it, it will not last for this period. 

The author stipulated that in the case of renting out
something for a period of time, he should think it most likely that the
thing will continue to exist during that time. If he does not think that it
is most likely that it will continue to exist, then the contract is not
valid, because the renter is not going to be able to make full use of the
item during that period, and one of the conditions of rental contracts is
that it should be possible to make full use of the item during the specified
period. However, if a person rents something out for a period during which
it is thought most likely that the thing will continue to exist, but it does
not, then the contract is nullified and the renter no longer has to pay rent
for the remainder of the period. 

End quote from ash-Sharh al-Mumti‘, 10/47

And Allah knows best.