ともなると / ともなれば

1. 1When a particular time, season, or event arrives, a situation typical of it naturally follows.Ex. 1
2. 2Once someone or something reaches a certain rank, status, or level, correspondingly higher demands or different circumstances apply.Ex. 2

A somewhat formal, written-leaning pattern, also heard in careful speech, used in commentary, essays, and observations about what comes with reaching a notable stage or position. The main clause can state a general tendency or an actual consequence, as in 「いざ本番ともなると、緊張して声が震えた」. Unlike だけあって, which evaluates a result as fitting what X is, ともなると highlights the shift that comes with reaching the stage.

• だけあってN2「だけあって」evaluates a specific person or thing that is already an established fact, saying the result truly matches its reputation, often with admiration, and it can also attach to adjectives. 「ともなると」, by contrast, gives a neutral, general statement of what naturally occurs at a given stage or status, so they generally cannot be swapped.
• にしてN1「にして」is close to this pattern only when attached to ages or stages: it describes the specific situation at that point in time (only after... did..., or at just... age one already...), in formal written style. 「ともなると」instead states what naturally follows upon reaching that stage, so they cannot be swapped.
• にあってN1「にあって」focuses on being situated in a special circumstance or position; it works with either continuing or contrasting logic, and the following clause may state how things should be. It attaches only to nouns and is written-style, whereas 「ともなると」emphasizes what comes naturally at that stage, also takes verbs, and is stylistically neutral.
• にしてはN3「にしては」takes the preceding item as a standard and points out that reality does not match expectations, carrying a sense of surprise. 「ともなると」says that reaching a certain stage naturally brings corresponding circumstances consistent with expectation—the two run in opposite semantic directions and cannot be swapped.
• ときたらN1「ともなると」neutrally describes situations that arise naturally upon reaching a special stage, attaching to both nouns and verbs. 「ときたら」attaches only to nouns and vents strong emotions—usually complaints—about familiar people or things in colloquial speech, so the two cannot be swapped.
• に至ってはN1「に至っては」requires first describing cases of the same kind and then citing the most extreme example among them, usually with negative judgment; it attaches only to nouns and leans toward written style. 「ともなると」simply expresses what naturally happens at a special stage in a neutral register, so the two cannot be swapped.

Unlike だけあって, which explains a result, favorable or not (e.g. 「安いだけあって、すぐに壊れた」), as matching what X is, and にしては, which marks something contrary to expectation, ともなると states what follows once a notable level is reached. にして stresses 'only at / even at this level', にあって means 'in this situation', ときたら introduces a topic in order to complain about it, and に至っては presents the most extreme case in a series.