I’m assuming the full years are needed for the alternative age calculation.

dogs =
   { Name: "Tom", Age: 25 },
   { Name: "Jerry", Age: 30 },
   { Name: "Spike", Age: 15 }
  ];

foreach dog in dogs
let avma = if dog.Age >= 2 then dog.Age * 5 + 14 else
           if dog.Age >= 1 then dog.Age * 5 + 10 else
           dog.Age * 5
select { Name: dog.Name, DogAge: dog.Age * 7, avma: avma }

Full transparency, I generated this with AI Assist with modifications to include Carl and MrTeeth in the data set to check my year 1 and 2 calculation and modifying the Select statement output to include the 7 year average age calculation (borrowed from @AndyL  - thanks!). 

/**
 * This query was generated by AI Assist.
 * As with most things AI, it may not always be completely accurate. Carefully review and verify it.
 * You can use it as a starting point and build on top.
 * Alternatively, you can try to refine your prompt and regenerate.

   / \__
  (    @\___
  /         O
 /   (_____/
/_____/   U
 */
dogs =
  b{ Name: "Tom", Age: 25 },
   { Name: "Jerry", Age: 30 },
   { Name: "MrTeeth", Age: 1 },
   { Name: "Carl", Age: 2 },
   { Name: "Spike", Age: 15 }
  ];

//
//// The first year of a dog's life is 15 human years
firstYearFactor = 15;

//// The second year of a dog's life is 9 human years
secondYearFactor = 9;

//// Each subsequent year is 5 human years
subsequentYearFactor = 5;
//

foreach dog in dogs
let age = dog.Age
let AVMAhumanYears = if age < 2
                 then firstYearFactor
                 else if age == 2
                      then firstYearFactor + secondYearFactor
                      else firstYearFactor + secondYearFactor +
                           (age - 2) * subsequentYearFactor
select {
  Dog: dog.Name,
  "Dog Age": age,
  "Dog Average Human Age": age * 7,
  "AVMA Age": AVMAhumanYears
}

Rather than a maintainable and comprehensible sequence of if-then-else clauses, we can be silly but terse:

dogs =
  [{ Name: "Tom", Age: 25 },
   { Name: "Jerry", Age: 30 },
   { Name: "MrTeeth", Age: 1 },
   { Name: "Carl", Age: 2 },
   { Name: "Spike", Age: 15 }
  ];

foreach d in dogs
let HumanAge = 15 * min([d.Age, 1]) + 9 * min([d.Age -1, 1]) + 5 * max([0, d.Age - 2])
select {Name: d.Name, HumanAge }

@musa shared another solution with me - this sleek Iverson bracket inspired script. 

given(booleanExpr) = if booleanExpr then 1 else 0;

humanAge(x) =  15 * given(x >= 1) + 9 * given(x >=2) + 5 * (x - 2) * given(x > 2);

dogs =
  /{ Name: "Tom", Age: 25 },
   { Name: "Jerry", Age: 30 },
   { Name: "MrTeeth", Age: 1 },
   { Name: "Carl", Age: 2 },
   { Name: "Spike", Age: 15 }
  ];

foreach d in dogs select {Name: d.Name, HumanAge: humanAge(d.Age) }

This was new to me so here’s a little background on Iverson bracket notation:

The Iverson bracket is a mathematical notation introduced by Kenneth E. Iverson, commonly used in combinatorics, linear algebra, and computer science. It is defined as follows:

"P]

where P is a logical statement or condition. The Iverson bracket evaluates to:

- 1 if the statement P  is true
- 0 if the statement P is false

For example:

• If x=5 then =x>3] becomes 1 because 5 is greater than 3.
• If x=2 then >x>3] becomes 0 because 2 is not greater than 3.

This notation is helpful for expressing formulas in a concise and efficient way, often eliminating the need for conditional statements.

I learned something - thanks @musa!