'slow' is an adjective not an adverb and would thus be grammatically incorrect
And if we had HE WANTS TO AGE IN A SLOW MANNER like definition 17, it would work.
\17. in a slow manner; SLOWLY
and you wanna say that "he wants to age in a slow manner" doesn't mean "he wants to age slowly"?
Lica, in the phrase 'in a slow manner", the word "slow" is an adjective. But the phrase as a whole is an adverbial phrase equivalent to "slowly".
In other words, when an adverb is required, you can use "slowly" or the entire phrase "in a slow manner", but in standard English you cannot use just "slow".
Lica, it is true that people speaking informal English will sometimes use as an adverb the adjective form (e.g., "slow") where standard English requires an adverb with the form in -ly (e.g., "slowly"), just as some people will say "wanna" sometimes instead of "want to". But the point is that those choices differ from STANDARD English.
The Czech in this DL course aims to be standard Czech (rather than Common Czech), and the English used aims to be standard English.
wow so I gave you link to a dictionary where it says that slow can be an adverb yet you continue to say that it can't be? you think you know better than the dictionary?