Have you talked to a recruiter yet about your wishes? The nuclear field does have an age requirement, this is the rules for it:
Qualifications. NF candidates must be U.S. citizens. Candidates must also not have reached their 25th birthday by the time they enter active duty (ship out to basic training). However, age-waivers will be considered on a case-by-case basis. Applicants must be a high school diploma graduate (not GED) with successful completion of one year of Algebra, and able to meet Secret
security clearance requirements.
So you might ASK if it is possible, but my guess would be not likely.