What's an idiom or word or name for an initial tester?

What would be an idiom or word or name for someone that is an initial tester (like a beta tester).

I am writing a speech for my younger brother's engagement and want to say how I have always been the first to try everything in my family--schooling, learning to drive, college applications, etc.--because I was the oldest son. My parents basically used me as a trial run to test the waters each step of the way in their parenting. They tweaked and refined the process with each of my two brothers.

Now for his wedding, he's being sent out to scout for the proverbial mines for the first time.

So I'm looking for a better term than beta tester to describe what I have been my entire life. I was kind of like a "lab rat", but that sounds horrible. Here's the line:

"Throughout our life, being the oldest, I was sent out as the front line to test the waters."

I really hate that line. I hope having a better term for "beta tester" would make that line make more sense and sound better.

Solution 1:

You could say you were a pioneer or trailblazer in your family.

"Being the eldest, I was a pioneer in many ventures. For example, my experience in schooling was tweaked to give my brothers a better schooling experience. My brothers avoided my mistakes while learning to drive. For my brothers, choosing colleges and filling application forms were a breeze, after my pioneering attempts."

In the previous sentence, change pioneer to trailblazer and see which you like.

If you prefer, you could add "accidental pioneer" or "accidental trailblazer", because you were not given a choice, and it was an accident of fate that you were the eldest.

Solution 2:

The term guinea pig according to etymonline.com

In the extended sense of "one subjected to an experiment" it is first recorded 1920, because they were commonly used in medical experiments (by 1865).

Also from Wiktionary:

De-classified documents of the National Archives revealed that during the 1930s and 1940s, the British Army used hundreds of Irish and native British Indian Army soldiers as "guinea pigs" in their experiments to determine if mustard gas inflicted greater damage on Indian skin compared to British skin. It is unclear whether the trial subjects, some of whom were hospitalised by their injuries, were all volunteers.[5]

In your speech you might use it as:

Throughout our life, being the oldest, I was always the guinea pig whether it was for going to elementary school, learning to drive, or filling out college applications.

Solution 3:

Vanguard might work with positive connotations of looking out for your little brother while welcoming him to engage the fray of marriage first:

noun

1.0 A group of people leading the way in new developments or ideas:
the experimental spirit of the modernist vanguard

1.1 A position at the forefront of new developments or ideas:
the prototype was in the vanguard of technical development

1.2 The foremost part of an advancing army or naval force.

ODO

Throughout our life together, being the oldest, I was usually the vanguard, but this time, you will be the vanguard!