My feeling is that In English the gerund has to refer to the subject, i.e. in this sentence the ”looking younger” refers grammatically to me and not to the man I chose. To make this clear it is more correct to say ”Since he looked youger, I chose him” or ”I chose him because he looked younger”.
That could happen in English. Romanian phrases can't be translated directly to English. That's why sometimes we get confused. For example in Greek (my native language) we use gerund the same way it is used in Romanian. ''looking younger'' refers to the object (he) of the verb (choose) and is the reason justifying the action of the subject (I).