Working on off-page SEO for the 9-year-old domain that is redirected may not provide significant benefits. The primary domain, which is currently 4 years old and functioning as the main domain, should be the focus for SEO efforts to maximize effectiveness.

Redirecting URLs don't get crawled and even domain age doesn't impact ranking.

The impact of redirecting a domain is useful if the domain has incoming links with traffic. And there is relevance between the domains. Best practice is to redirect not the complete domain at once, but relevant pages. So a visitor gets where he is looking for.

Working on off-page SEO for the 9-year-old domain, even if it's redirected, can still bring benefits and contribute to overall SEO strength.

i have 2 domain 1 is 4 year old and other is 9 year(redirected) old. currently my main domain is 4 year old (working as a main domain). Should i work offpage seo on 9 year old i will benifited or not it is rediceted.