But it works other way, But for some other natives with gemini ascendant with strong second house works properly.
Additionally following link explains why to start from strong of 2nd house or 8th house,
http://astroveda.wikidot.com/shoola-dasaBecause the 2nd and 8th rasis in the natural zodiac are owned by Mars and Venus, rasi aspect on either of them by Moon generates Rudra yoga and rasis aspected by Rudra yoga planets can give death.
if 3rd house and 8th house represents longevity and hence 12th from those two houses are maraka houses (2nd and 7th), But why to start from 2nd or 8th instead of 2nd or 7th is not clear.
Generally excluding certain conditions like balarista etc, each planet is capable of giving certain ayush to native, but this dasa focuses more only on Rudra and maraka alone. And certain good yogas (panch mahpurush yogas) etc, denote purnayu and ayush of 70 year etc, Does this dasa over rule all such conditions?