Impossible to say. The planets of our solar system were created at about the same time. About 4.5 to 5 billion years ago.
Each day it gets one day older, that would mean that over the course of a year the planet would become a year older.
Mercury is the planet with an 88-day year.
No one knows for sure yet. Some day Mercury can become a drawf planet because of how small it is. If Mercury does become a drawf planet Mars is probably next.
The planet Mercury has a day that is almost the same length as its year. Mercury's rotation period is about 59 Earth days, which is very close to its orbital period around the Sun of about 88 Earth days. This means that one day on Mercury is almost as long as one year on Mercury.
Mercury's "sidereal day" is about 59 Earth days long and its year is about 88 Earth days long. Venus has a "solar day" of about 117 Earth days and a year of about 225 Earth days.
Mercury has the shortest year of any of the planets. It is only 88 days. Mercury's day takes 58.646 Earth days.
That's Mercury: "sidereal day" is more than half its year. Or, it could be Venus: "solar day" is just over half its year.
It's Mercury or Venus, depending on which definition of "day" you use.
Mercury is the hottest planet, because it is the closest planet to the sun.
Mercury has a year that is shorter than its day. It takes Mercury about 88 Earth days to orbit the Sun, but it rotates on its axis so slowly that its day is much longer, lasting about 176 Earth days.
Mercury's day is about 58.65 Earth days, and its year about 87.97. Venus has a day that is 243.0 Earth days long, while its year is only 224.7.
Mercury's year of 88 days is pretty short when compared to Earths 365 day year. The orbital period gets longer the further you go out. Neptune is the furthest planet out and takes nearly 165 years to go around the sun once.