Год, года, году, годом, годе are all singular (in nominative/accusative, genitive, dative/locative, instrumental and prepositional respectively).
Лета, лет, летам, летами and летах are the irregular plurals of год in different cases (nominative/accusative plural, genitive pl, dative pl, instrumental pl. and prepositional pl.).
With numbers ending in один (‘one’), use год: один год, трицать один год.
With numbers ending in два to четыре, use года (genitive singular): четыре года, двацать четыре года, восемьдесять три года.
With numbers ending in пять to девять – and also higher numbers like сорок, сто and тисяча, use лет (genitive plural): девять лет, сто (100) девять лет, четырсот сорок пять (445) лет.
If you are having more troubles with numbers and cases, and years, you can check out this playlist called ’Managing Numbers in Russian’ by the YouTube channel ‘Russian Grammar’.
Я and ты become мне and тебе. Мы and вы become нам and вам. You might have noticed that the pairs я/ты, мой/твой, мы/вы, наш/ваш generally have very similar forms.
Он, она and они follow a different pattern (the one adopted by adjectives, with some changes): он/оно→ему, она→ей, они→им. Do not forget that all of them require an initial н after simple prepositions (e.g., к нему)—though, there are only two simple Dative prepositions in Russian (к and по).
Feel free to memorize the forms you expect to use the most.
Сколько means "how many/how much". When saying someone's age, the person is in the Dative. Then you say the number of years (it is the subject of the sentence:
- Кошке два года = The cat is two years old.
- Моему сыну три года = My son is three years old
- Мне двадцать лет. = I am 20 years old.
- Ей пять лет. = She is five years old.
- Ему восемнадцать лет. = He is 18 years old.
- Маме тридцать пять лет. = Mom is 35 years old.
I do not feel like saying that Сколько тебе лет? is literally "How many years is to you?" because, well, English does not use this structure much (therefore it hardly has any meaning). In Russian, though, certain words that mean states and emotions are applied to a Dative "experiencer".
We do not explore Dative forms in much detail at this point in the course. If you really need to know, the Dative forms of Russian personal pronouns are as follows:
- я → мне
- ты → тебе
- он, оно → ему
- она → ей
- мы → нам
- вы → вам
- они → им
Dative forms of adjective and adjectival words are a sure overkill but if you need them, they end in -ому(ему) for masculine/neuter agreement, -ой(ей) for feminine, -ым(им) for plural.
Thanks! I would not expect to translate this literally but it does help to know what the sentence actually means and not just the English equivalent - much like the possessive sentences mean "By x there is y," even though we do not express it this way in English. A literal translation is helpful in remembering which case should be used and why.