Maths Question of the Decade

In about October time, someone twigged on that the decade was coming to an end. All we've heard since is 'decade', 'decade', decade'...

As it's my daughter's birthday, my mind shifted to a possible maths problem... (in a similar fashion to the Birthday Riddle): 

So, I'm 36 and I'm entering my 5th decade. 36 and 50 (ie 5 decades) are a fair distance apart. The children currently in Years Four, Three, Two... are only just entering their second decade.

So, here's the question:

How long would someone have to be alive to enter their second decade at the earliest opportunity?

How long would someone have to be alive to enter their second decade at the latest opportunity?

How long would someone have to be alive to enter their fifth decade at the earliest opportunity?

How long would someone have to be alive to enter their fifth decade at the latest opportunity?

How long would someone have to be alive to enter their tenth decade at the earliest opportunity?

How long would someone have to be alive to enter their tenth decade at the latest opportunity?

Or, any other similar questions that may come to mind...

What's the longest a decade can be? What's the shortest a decade can be? (NB: Leap Years ;-))

Órlagh's Birthday Riddle

Yesterday, my daughter celebrated her second birthday and today she's in the fourth year that she's been alive. How can this be true?

It is true, I know 'cos it's my daughter. I'm going to give that statement to my class this week to see if they can figure out how it can be true.

In case you hadn't already worked it out... She was born on 31/12/2014. She therefore spent sometime (not much) in 2014, also 2015 and 2016. As it's now 2017, that's a fourth (calendar) year. The years are actually irrelevant as the answer is she was born on New Year's Eve and two years and one day later, it's now New Year's Day.