I've never known a Nathaniel myself so I can't answer that question. When I was about 20, Nathaniel was one of my favourite names and when I was imagining what my Nathaniel would be like, I pictured a redhead (possibly because the first Nathaniel I ever heard of was the one on Promised Land, or possibly because I had a big crush on Rupert Grint at that time in my life, hahaha), and bookish. I don't think I would have said "wimpy", because I don't find Daniel or Nathan to be wimpy, but I do think they're soft and smooth... this is a good thing.
I definitely don't think Nathaniel would be wimpy, but for some reason, I don't really picture a jock being named Nathaniel... however, Nathaniel easily lending itself to Nate, I see that as a more "athletic" name, but obviously a Nathaniel could be an athlete, a math wiz, an artist, an adventure-seeker, or anything else. Each kid is an individual, and I've never come across any name where *everyone* I've met with that name has been exactly the same. I had 12 students named Mikel last year and each one was very distinct.
My little cousins name is Nathaniel, and he is the sweetest kid on earth!
We have friends who just had a Nathaniel and he is darling! Of course, he's only a month old.
I knew several Nathaniels when I was teaching. One was somewhat handicapped but the toughest (in a good way) and most determined boy I ever had in any class. I cherish the letter he wrote me to this day. Another was a kind and thoughtful little guy who grew into a kind and thoughtful teenager.
Its not their names that make them who they are.
My cousin is Nathaniel and I know a little Nathaniel both called Nat. My cousin I haven't seen for years as he lives in Melbourne but the little one is crazy.
Its still a great name.