forgetting the old year's troubles
Refers to putting aside the hardships of the passing year, often in the context of year-end parties (忘年会).
At the year-end party, we forget the hardships of the past year.
forgetting age differences
Describes a social atmosphere where people of different ages interact without regard to age hierarchy; often associated with 忘年会.
They form a friendship that transcends age differences.
year-end party; bōnenkai; "forget-the-year" party
Compound of 忘 (forget) and 年 (year). The meaning 'forgetting age differences' likely developed from the idea of setting aside formalities at year-end gatherings.