OP here. Yes, this is one of my concerns. Actually, it appears that I'm the only one who is worried about this. My son, my husband, and his teacher are all thrilled. I'm happy as well, but I didn't realized that we were going to be making decisions about high school credit while he is still in elementary school. My son already knows how to do Algebra and he thinks its so easy. Math always came natural to him. He is a die hard STEM kid. His interests are medicine and engineering. However, he gravitates more to medicine. My other concern is that in 8th grade he will have to take math at River Hill School which isn't our zoned high school. I will find out next Monday more detail information at the Middle School Accelerated G/T Mathematics Orientation for parents. I already have a long of list of questions to ask at the orientation. Maybe I'm worried for nothing, but I still have reservations.
I'm looking at the letter right now and this is the breakdown of the accelerated math program:
Grade Level/ Course
6th- Algebra I G/T
7th- Geometry
8th - Algebra II G/T
9th - Precalculus G/T
10th - AP Calculus AB
11th - AP Calculus C
12th - AP Statistics, and/or Discrete Mathematics, and/or Differential Equations
NP (and I didn't read everything else)
Take a deep breath - it will be fine.

If your teacher is thrilled, your kid is well placed. Algebra 1 is the same course across the state, and your child will most likely find it boring. If they are in the G/T class, they will get extensions.
My DC1 had this pathway in MCPS:
6th- Algebra I
7th- H Geometry
8th - H Algebra II
9th - IB Precalculus
10th - AP Calculus B/C & AP Physics C & AP Statistics
11th - Multivariable Calculus (MVC)
12th - IB HL Math
DC2 has almost the same pathway, except he skipped a grade. So he started taking the classes at the same age as DC1, but one grade level later (Algebra 1 in 7th), but he still has ended up being compacted into a combo Alg2/precalc in 9th grade and will take Calculus in 10th grade still.
The typical way that MCPS handles 8th grade Algebra 2 is the students takes the bus to HS for math 1st period, and then there is a school bus to take the kid back to their middle school after HS 1st period, in time for MS 2nd period. HCPS sounds similar. Just make sure you understand the plan, but your child won't be the first to do that. Your list has options for speeding up or slowing down in high school - you can make those decisions later.
Congratulations!