This is from a Chinese novel I'm reading but I don't understand what this means. I tried translating and I know 装 should be pretend in this context but it doesn't make sense to me when fully translated (pretend is not so pretend).
I just saw @imkzh's comment saying that 装 here means 装B. We need more background of the characters involved or the scenario where it's spoken to understand it. In general I think the implication is too strong for a written work. Seeing the sentence alone, 装 could be more close to that of 装模作样 (behave in an affected way), which can also be expressed by the English "pretend".
也 is used for emphasis in negative sentences.
是 is a copula, but here it has a slight shade of "should be". 不 negates it.
是……的 is similar to "it is ... that" as a construct for emphasis. Ex. 我吃了饭 vs. 我是吃了饭的. The latter emphasizes on the fact of 吃了饭.
这么 is a demonstrative pronoun used adverbially, modifying the second 装. Together, it's "pretending in this way".
The first 装 is the topic, 也不是这么装的 is the comment.
Word for word, it's then "As for pretending, (Subject) should not be pretending in this way".
I would agree more on @imkzh's answer. Here the relatively understandable way to translate for the full sentence is that:
"He could already live until 200 years old"
"and he's still saying that his life is short"
"That is not how one shows off."
Pretending is still slightly different from what 装逼 means; it's more of an act of bragging and showing off in Chinese popular culture as similar to what @imkzh said.