Mental Math for Lamb 1

Lately our math program has had a line to write the 2 digit addition or subtraction problem horizontally. After the easy ones such as subtracting 10 from a number, I asked Lamb 1 to write the problem vertically in the space beside the problem. I expected him to do this and show his work so that if he made a mistake he could see his mistake easier than if it was written horizontally and the work was done in his head. He did what I asked and then erased his work done on the side of the page. I have asked him several times to show his work and he always erases it when he does. Slow Mama finally figured out that ALL the problems are easy to do in his head. He's embarrassed to have to show his work on the side. He always gets them right when he does them in his head so he doesn't understand my telling him to show his work in case he makes a mistake.
Today's math was to make a graph of when some real pennies were minted. We began by looking at each penny and making a tally mark for the year it was minted. When he was making these tally marks instead of saying out loud what year it was, he would say things like "the year that Mama was 24" or "5 years before I was born". I consider this some higher level mental math for a 7 year old! Not only did he not just answer the year, but he was subtracting 2 digit numbers like 97-73 and in a few cases he was even subtracting 2000's-1900's (which is something that I always have to think twice about to make sure that my mental math is correct). Plus when he was told once the year that our birthdays were, he never forgot. I always ask him how old family members are going to be when I'm writing out birthday cards, he knows how old his grandparents and great-grandparents are (or the ones in heaven how old they would be).
Age wise Lamb 1 will begin second grade in the fall. In math we have completed 2/3 of Saxon Math 2. I don't think we will finish Math 2 this summer, but we should have most of it done. So shortly after he begins second grade, he will begin 3rd grade math. Even working a year ahead in math, it is too easy for him. So what does he do? Makes it into a challenge instead of answering the year of the penny and answering a year relevant to our lives.  For reading and writing, he is just an average just finished first grader. But he does so well at math that it seems like he is behind to me in those other subjects. I have to remind myself that he is doing fine in those subjects.
When I taught in the classroom, there were a few students that I let work a year ahead in math. They pretty much worked on it on their own and I graded it. There were a few students that went to the next grade for reading class. But there is no way in the classroom to totally fit the student to the entire curriculum at which level they need to be. In homeschool Lamb 1 is a year ahead in math and right on schedule for reading and writing. We do spelling totally at his level-he works on the words that he needs to work on and skips the words that are easy for him.
Math is even easier for Lamb 2 so I'm not quite sure how he is going to make it into a challenge. Age wise he will begin kindergarten in the fall. He has already began a first grade math book. He wants to know how to read and he tries at simple books, but it hasn't clicked yet.
Lamb 1 and 2's abilities show me one more reason why I'm glad we homeschool.
Note: Lamb 1 is doing math this summer because we took off so much time for Ram's surgery last fall. We are doing a little other school this summer so they don't forget what they learned last year. We are also reading a lot of books. School time is very short this summer and then they have the rest of the day to play!
Note 2: This is not so much a brag post about the Lamb's math abilities, but I want to document this for my memory of Lamb 1's math ability at age 7.