Julius Caesar declared that the year started on January 1st, or so it was told to me. January is named after the Janus, who having two heads/faces also has two sets of eyes and can look backward and forward at the same time. Janus was the the Roman god and guardian of gates and doors, beginnings and endings and Janus also governed the transitions of life. the transition from primitive to civilised, rural and city, war and peace, and the stages of life, birth , adolescence maturity and death. And perhaps in choosing that Caesar was acknowledging the parralell between the seasons and a life.
Though our calender year starts on the 1st of January, in other cultures it starts with the spring rains, or the autumnal dry season. Or possibly on the date on which someone started their sober life, Samhain ends the Celtic year, Christmas Day marks the passage of a year for some, clearly the beginning and ending of a year can be and has been marked in many different ways.
The year is very simply a measure of time, as in the commitment "a year and a day", or in the time it takes the earth to circle the sun. Unlike the calendar year which always starts on Jan 1, in a year we define for ourselves we might hope to accomplish some task, or learn some skill, but still if this doesn't happen we have not failed, our resolution may not have been successful, but that doesn't mean that we cannot start all over again, the next day.