Justin Trudeau is now the old man of the federation — and he didn't have to wait very long

When Iain Rankin was sworn in on Tuesday as Nova Scotia's new premier, Prime Minister Justin Trudeau became something very few prime ministers become, something none of his predecessors became at such a young age — the person with the most experience at the table.

With the retirement of former Nova Scotia premier Stephen McNeil, Trudeau is now the senior figure in the federation. No provincial or territorial premier has been in government as long as Trudeau has been prime minister, even though he started in the job little more than five years ago.

That makes Trudeau just the sixth prime minister ever to become the longest-serving sitting government leader in the country. It also puts him in a club with some accomplished members: the other PMs who hit that longevity mark before leaving office were John A. Macdonald, Wilfrid Laurier, Mackenzie King, Pierre Trudeau and Stephen Harper.

Unlike those five, however, Trudeau hasn't had to wait very long to become the last person standing.

No other prime minister (with the exception of Macdonald, who by default was the senior figure nearly from the start) has served for less time than Trudeau before becoming the most seasoned leader in the country.

Trudeau has been in office for just 5.3 years. Harper — who previously had been the prime minister who had the shortest wait to seniority — was starting his seventh year in office when he became the longest-serving leader in the federation in 2013.

Trudeau's father had to wait over a decade. Pierre Trudeau was also nearly 60 when he took over the mantle of Canada's senior political figure, while both King and Laurier were over 60 when they reached the milestone.

Justin Trudeau is just a little over 49 years old — a few years younger than both Harper and Macdonald when they achieved seniority.

Since 1867, the average age of the senior figure around the first ministers' table has been around 55 years old, making Trudeau one of the younger oldest-hands in Canadian political history.

Even in the current context, it might seem a bit odd that Trudeau's longevity is greater than that of his provincial colleagues. Only Rankin (37), Newfoundland and Labrador Premier Andrew Furey (45) and Saskatchewan Premier Scott Moe (47) are younger than Trudeau.

Few premiers have reached seniority faster than Trudeau

In fact, for most of Canada's history the longest-serving sitting government leader has come from a provincial capital rather than Ottawa. That makes Trudeau's quick rise to seniority even more of an oddity.

Only two provincial premiers have served for less time than Trudeau before becoming the most experienced leader — and the last one served nearly a century ago. Former British Columbia premier John Oliver waited just 4.9 years before becoming the senior figure in the federation in 1923, while New Brunswick premier George E. King did it in just under three years in 1875.

On average, premiers and prime ministers have had to wait about nine years to achieve senior status — enough time to cover at least two governing mandates. Trudeau is only a third of the way through his second term in office.

Former Quebec premier Robert Bourassa had to wait the longest before getting to the head of the table. He became the senior figure in 1990, about 20 years after his first election win in 1970.

Of the 43 people who have held senior status since Confederation, only eight premiers were younger than Trudeau when they reached the top of the mountain. They include New Brunswick's Frank McKenna and Richard Hatfield and Alberta's Ernest Manning.

Seniority is fleeting

On average, Canada's "senior statesman" (and it has only ever been a man) has held the title for just 3.7 years. Trudeau will have to hold on to his job until November 2023 to pass Harper and avoid becoming the prime minister who has been the senior figure for the least amount of time.

Macdonald, of course, holds the record — nearly 19 years spread over two non-consecutive periods in office. No provincial premier has broken that record, though Manning came the closest. He was the senior political figure for nearly 15 years between 1954 and 1968.

Manning was also the last figure to hold the title for more than seven uninterrupted years. Why? The past few decades have seen a lot of turnover among premiers and prime ministers. The last person to be the longest-serving governing leader for more than three years was Alberta's Ralph Klein, who stepped down as premier in 2006.

Trudeau is the 12th person to hold the senior status title since Klein retired from politics. Compare that to the relative stability in federal and provincial leadership between 1927 and 1968, when only four leaders sat as senior figures: Quebec's Louis-Alexandre Taschereau, Nova Scotia's Angus L. Macdonald, King and Manning.

Trudeau has seen his fair share of turnover during his relatively short time in office. Rankin is the 27th provincial or territorial premier Trudeau will get to know.

That might sound like a lot — but King, Macdonald, Harper and Jean Chrétien each saw at least 40 premiers and territorial leaders come and go. Trudeau might still have to make it through another election or two to get into that company.