Short answer :
Its all false and fabricated accusations on AYATOLLAH KHAMEMEI...
If you want Clearification.. Read the Long Answer:-
(Dont Spread Flase and fabricated Accusations.. You have to die some day)

Long answer:
Every Shia Ayatollah who wants to become a ''religious leader''(or a "'Marjae Taghlid''), someone who is able to give religious advice to others, has to write an extensive religious text called a ''Resaleh'', and in it explain his own opinion concerning religious, ethical, philosophical, social and political matters. In this text a lot of ''possible scenarios'' are considered, and a lot of questions are answered on how a good Shia should deal with those scenarios if they ever do happen.

This ranges from simple matters like what should one do during Ramadan if he's a traveler, to complicated things like how to deal with people from other religions, to ridiculous things like what you should do if you fart during prayer or have an erection while reading the Qoran!

Khomeini was both a Grand Ayatollah and a Marjae Taghlid, so he had his own "Resaleh'', which is very elaborate and extensive. To non-Shia Muslims some of the things in his Resaleh might sound ridiculous. some of it might sound bizarre and some of it will sound other-worldly. I am Shia but I don't follow Ayatollah Khomeini as my mentor,however I have read some of his Resaleh and to answer your questions one by one :

sex with females of any age if they were promised in marriage.

He says it is best not to have sex with women under the legal age of consent in Islam, which is 9 for women and 15 for men, because formal marriage is impossible before this age, but if such a thing happens between a boy and girl who have been engaged, it is not considered ''Zenae Qeir-Muhassenah'', or ''grave adultery between unmarried couples'' which is considered a great sin, and could be punishable by lashes.

also brought quotes saying he approved of Opium use

No, he absolutely did not approve of it, he believed it was not a sin.

To understand this perfectly, you must consider the differences between a bad act, the law, and a ''sin''. Sin is a bad act you commit against God and his will, it is a religious concept. Bad behavior is something you do to other people that is not acceptable under the ethical belief system and cultural climate you live in, or that is hurtful to others. Law, is a government mandate for how you should behave based on legal considerations. Opium and other narcotics are illegal in Iran, and people dealing more than a certain amount of it will be executed by the government, using them is also a social stigma and is not considered ''good'' or ''acceptable''. So it's not good, it's not legal, but is it a sin against God and his true prophet? Each Ayatollah has a different answer. Khomeini thought that even though narcotics are socially destructive and using them is a morally reprehensible thing to do, it cannot be considered a sin because sin is by nature determined by God.

Using opium and other drugs is not considered a sin in Islam because when Muhammad (s) was chosen by God to become a prophet these things did not exist.

sex with animals

Absolutely not. As I mentioned earlier, an Ayatollah must answer every question that his followers ask from him, and he has to come up with an appropriate punishment for each sin from a religious point of view. Having sex with animals is a sin, illegal, and a morally wrong thing to do. All three. But ''what if'' someone does have sex with a animal? What should that person do to repent? Confess to God, pay some fine to the owner of the animal and pay a fine to the local mosque, was Ayatollah Khomeini's answer. Some misguided and judgmental people took this as ''Khomeini is saying pay some money and go Bleep a goat, look at this depraved pervert''. But of course this is not true or fair.

An Ayatollah has a moral responsibility and a religious duty to answer every single question that a believer might have from him, a Resaleh is a thick book filled with these questions and the author's answers to them. So he's not saying ''Mmm yes, let's go Bleep some goats right noaw'', he's saying ''what if someone bleeps a goat..'

Some of our kafir friends have had great times trolling these pious old men with questions like ''what if I sit on a spoon and it ends up my rectum'', ''what if I accidentally marry my mom?'', ''what if I piss out of my ass one day and it ends up in my mouth?'', ''what if alines come to earth and I Bleep one of them, is it halal?''... The kafirs do this for several reasons: to mock our faith and show how ''silly'' we religious folks are(and how enlightened they are), to give the less intelligent fedora tippers something to mock us instead of having a civilized discourse, and also because it's ''fun'' to mess with the holy.

And they have answered them all! In fact you can ask these questions from most Grand Ayatollah's online, and they will answer almost all of them no matter how ridiculous they might sound.