。
I've known for ages that this guy isn't that kind of person.
Literal
This-guy [subj-が] that-kind-of gem [copula-ではない] thing [such-things-なんて] long-ago [gen-の] past [to-に] understood [because-から] [casual-さ].
そんな玉じゃない uses 玉 (たま) as slang for 'type of person / caliber' — literally 'gem/ball,' figuratively 'the right sort.' とうの昔に 'ages ago / long since' is a set temporal adverb. なんて dismisses the proposition as obvious. The さ at the end is a casual masculine sentence-ender adding a nonchalant, 'it's-no-big-deal' tone.