春機が発動して、ソレをナニしたい盛りなのは理解するけど、・・・まあ、そこにお座りなさい。

、、・・・、。

I understand you're at the peak of puberty and all worked up wanting to do 'that' to 'that thing,' but... well, have a seat here.

Literal

Puberty-urges [subject-が] activate-[and-て], 'that' [object-を] 'that-verb'-want [peak-盛り] is-[nominalizer-なの] [topic-は] understand [but-けど], ... well, there [to-に] [honorific-お]-sit-[gentle-command-なさい].

An adult awkwardly addressing a young person about sexual urges. 春機 is a rare, literary/classical word for 'sexual urge, puberty-drive' (春 'spring' — a season associated with romance/fertility — + 機 'opportunity, mechanism'). ソレ and ナニ in katakana are deliberately vague demonstratives for things the speaker doesn't want to name — 'that' and 'that thing / do-whatever' as coy stand-ins. 盛り ('peak, height of X') attaches to nouns for 'the X-prime of life.' お座りなさい is the gentle parental command 'sit down.'