Adding punctuation, your sentences are as follows:

[黄金聖闘士]{ゴールドセイント}十二人とはいえまだ幼い者がかなり多い。[白銀聖闘士]{シルバーセイント}、[青銅聖闘士]{ブロンズセイント}しかりだ。

…(も)しかりだ means “so is ….” In your case, the speaker says that most of the twelve Gold Saints are young (implying that they are too young for the duties), and then he/she says “So are Silver Saints and Bronze Saints.”  (I am not sure why the speaker says 十二人とはいえ in the first sentence; interpreting it needs more context, and I will not try it here.)

As Jesse Good wrote, [然]{しか}り means そうである. It was originally a verb, and could not be followed by だ, but in modern Japanese the form しかりだ is often used.

Adding punctuation, your sentences are as follows:

[黄金聖闘士]{ゴールドセイント}十二人とはいえまだ幼い者がかなり多い。[白銀聖闘士]{シルバーセイント}、[青銅聖闘士]{ブロンズセイント}しかりだ。

…(も)しかりだ means “so is ….” In your case, the speaker says that most of the twelve Gold Saints are young and immature, and then he/she says “So are Silver Saints and Bronze Saints”; in other words, “Also most of the Silver Saints and the Bronze Saints are young and immature.” 

(I am not sure why the speaker says とはいえ in the first sentence. Interpreting it needs more context, and I will not try it here.)

As Jesse Good wrote, [然]{しか}り means そうである. It was originally a verb, and could not be followed by だ, but in modern Japanese the form しかりだ is often used.