Hello again, Colin!
Your mother is right, it is an ancient symbolism indeed, christian religion is not the oldest, but it does go back to medieval times. Even before the idea of god existed, people praised the sun!
Wether it has religious connotations or not, the main focus of the game is not religion itself, so it's normal you think the puzzle might have been delivered to a very specific audience; though, i must say, the riddle could still be solved by using logic.
Are you familiar with the Uncharted game series? Lots of ancient symbolism are added there which, if you know of, can help you solve the puzzles faster, but the game itself was designed so anyone could do it. It's like an inside joke, if you get it, you'll feel good, but if you don't, you'll just have to think on the logics of the puzzle itself.
The riddle talks about a sacrifice of love, a sacrifice of pain and a sacrifice of faith.
Blood is an organic thing, belongs to our "Body". By simple association you can figure out this could relate to the heart item.
The second altar was called "Mind", the riddle said something about pain, by deducing amongst the three other items you could think the crown of thorns is the most relatable, as it is worn on one's head.
Faith, you don't have to be a christian to know it is associated with the matters of the Soul. Thus, it was normal to put the cross, a sacred symbol in there.
I won't lie. The story has many concepts for a mature audience to enjoy, such as secret symbols and philosophical/psychological references.
But it is the characters and the adventure who also promises an interesting ride for people of any age.
If you still felt the game was in some way not suited for a certain audience, it is something i will have to work on in a later version of the game.
As for the concept and the game experience, it is meant to be played by everyone. Regardless, i appreciate your feedback and it will be taken into account. Have a good one!