Longevity of a chart should not be even mentioned (predicted) till the 24th year is completed which is the janma-riṣṭa period Maharsi Parasara
Bala-riṣṭa » 12 Years | riṣṭa associated with Moon as significator
Yoga-riṣṭa » 20 Years | riṣṭa associated with Jupiter as significator
Janma-riṣṭa » 24 Years | riṣṭa associated with Sun as significator
Study the following lessons carefully so that you know how to look for riṣṭa in a chart.
Duṣthāna Vakra-Graha
Durmantra
Tri-pāpa and Catur-pāpa
Maraṇa Kāraka Sthāna
Other Combinations explained
Tamas Chandra
Vināśa Yoga
Ardha Chakra
Shadow of Sun etc.
Things you need to study outside of BPHS
Tri-Pataki Chakra
Bear in mind that Neṣṭā Karma and Neṣṭā Graha require considerable understanding as these planets can surely give marriage and make life a wonderful experience or the converse i.e. living hell.
