I hear what you are saying. While we all want electives for all ages, we also want those electives to be age appropriate. Many elective awards have requirements that change based on Rank/Age,many others have the same requirements for all Ranks/Ages, and a few have Rank/Age restrictions. As such the Nova Awards are restricted to only be earned by Ranks/Ages Wolf and above. This is how an effective program offers electives for all ages. It offers diverse electives with varying levels of difficulty.
The Nova Awards are not designed or meant to be be completed in one Den meeting. They are not even designed with group completion in mind. They are meant to be an individually earned award on the Cub Scouts own time and ability. This is one reason Nova Awards use the concept of Counselor instead of Den Leader. I do agree that the Nova Awards can be too challenging for some Wolfs, Bears, etc. due to age, personal ability, and desire to engage in STEM. But there are some Wolfs that are passionate and ready for the Nova Awards.
When we have Cub Scouts interested in the Nova Awards, our Pack reaches out to all the eligible Cub Scouts to see if they are interested and what Nova Awards they are interested. Some do a specific Award on their own with a Counselor, usually me but not always. Other times we have multiple Scouts working on the same Nova Award. When I am the Counselor, I usually promote the group Nova Award sessions as an alternative Pack Summertime Activity. I will meet with the Cubs Scouts for about an hour at least 3 times, June, July, Aug. Most of the work they do on their own with their parents and then they discuss what they have done with their Counselor. When I am their Counselor, I strongly encourage they keep a Nova Award Science Journal, but do not require it. They are allowed to use their personal journals when discussing their work with me. I have no issue with a Scientist that takes, uses, and refers to their own notes when talking to a Mentor.
FWIW, I have been a Mentor to 9 (3 Cub Scouts, 6 Webelos) Supernova Award recipients from at least two different Packs. I have Mentored more, but some chose not to complete their Supernova Award and moved on to other activities more to their passions. And that is absolutely OK. I have directly mentored at least two other adults that went on to become Supernova Mentors.
My biggest complaint about the Nova Awards and Supernova Award program is that the requirements become very repetitive. Especially for those striving to earn multiple Supernova Awards. But that is how science works. It builds on repeating what you did before with greater outcomes.