"He wants to age slowly."
Translation:Chce stárnout pomalu.
Is this connected to this sentence or why are you commenting here? It is confusing.
Anyway, first accept that we are teaching the Czech word here, not the English one. So it must be "snažit se", the question is just how to translate it to English. Although I do not like pointing to translation dictionaries, I think this is a good place to do that, so check, for example, https://slovnik.seznam.cz/en/?q=sna%C5%BEit%20se try (hard) is the first translation there.
But explanation dictionaries are obviously better, so let's look into Merriem-Webster, my favourite:
Choose the Right Synonym for try, Verb
attempt, try, endeavor, essay, strive mean to make an effort to accomplish an end. attempt stresses the initiation or beginning of an effort. will attempt to photograph the rare bird try is often close to attempt but may stress effort or experiment made in the hope of testing or proving something. tried to determine which was the better procedure endeavor heightens the implications of exertion and difficulty. endeavored to find crash survivors in the mountains essay implies difficulty but also suggests tentative trying or experimenting. will essay a dramatic role for the first time strive implies great exertion against great difficulty and specifically suggests persistent effort. continues to strive for peace