From what I can tell, 一个年 is completely wrong because you can never use a classifier together with 年. The situation is different from a phrase like 一个朋友.
My question is: why? Is there a reason why 年 is different from 朋友 like this? Are there other nouns which behave like 年?
Or is 年 really syntactically more like 个? Is 年 actually usable as a measure word? Can you for example say 一年时间 or 两年工作?
You cannot say 一个年, but you can say 一个年头
The difference between 年 and 年头 had been explained here Understanding 年頭 in context
Yes, 年 itself can be a classifier '一年时间' and '两年工夫' are both valid
As the other answers said, 年 is a measure word when it refers to 'year', i.e. 一年时间, 两年工作.
Well, when 年 is used as a noun, it specifically refers to the Spring Festival, 新年.
For example,
你在中国过了几个（新）年了？ // How many Spring Festivals have you spent in China
这（一）个年怎么过 or 这（一）个新年怎么过 // How are we going to celebrate this Spring Festivals?
Because 年 is a count word or classifier. In our language it is called 量词. You can't use a count word to count another count word, like we never say 一个粒 or 一条只. But you use the double count words to express every, like 一年年 means every year.
