In order to qualify for ILR, your son would need to gain ILR before marrying and becoming financially independent. He would apply for naturalization on his own right, not as your dependent, and so he can become independent as soon as he has ILR.
How can the dependent of a tier 1 investor visa become independent without impacting his immigration status?
Our family applied for the tier 1 investor visa three years ago and successfully got another two years of extension. My son is a 21-year-old college student who is financially dependent on us. We were told that to keep his eligibility of applying for indefinite leave to remain, he would have to stay unmarried and dependent on us. When can he become financially independent without impacting his ability to apply for ILR and citizenship?