Never personally been to Suwannee, but if it's like almost any other resort I've been too......there will probably be a few others in your age range, but not that many. The median age will be much older.

The youngest trending resort I've ever been to is Caliente, about 2.5 hours south of that in Land O Lakes. Weekends there, you would be right about average age. If you're really worried about age that much, Caliente would be your answer. I recommend Sundays.

In any case, go on a weekend. Many more people there, so much higher likelihood that at least some will be similar in age. Weekends are also the time when more non-retired people (i. e., younger) are not working.

All of that said, age doesn't matter THAT much. I understand you're not interesting in hanging out with your grandparents, but there is both young and young at heart. Plenty of nudists in their 50s that fit that second description.