First off, while 年華 and 年 both translate to 'year', they have different connotations.
年華 is very poetic, and is usually used to reminisce the 'good old days', or refer to enjoyable times (not necessarily by year). 年 on the other hand is just a neutral word for 'year' with no special connotations. With that in mind I think it's clear why this sentence you have used 年華 but not 年.
Regarding the one character vs two character use, there are lots of reasons. My explanation above has already provided one of them -- as you have also suggested -- they could mean the same thing but have different connotations which will suit different contexts better.
Another reason is for clarity. Many a time one character words have multiple meanings, which could be ambiguous. In these cases, a two character word may be necessary to improve clarity. For example, 倒 can be to reverse, or to pour something out, or to have something collapse. So in contexts where all 3 meanings are possible, clarity can be improved with 2 character words that scope the meaning to just one of them. Eg. 倒車，倒水，倒塌.
One last reason I can think of is rhythm. Chinese as a language is very particular about 'rhythm', especially in writings where things tend to be more elegant, refined and 'flowy'. Now because usually a single character (and hence a single 'sound') cannot form a single rhythmic unit, 2 character words are usually preferred. In speech it's common to ignore this because of convenience, but writings are very much influenced by this.