The way you are asking your doubt is not like in other sciences. You have to give your date, time and place, so that your doubts can be resolved.
As you said Jupiter is the lord of 7th, which is maraka and badhaka to Gemini. But that Jupiter is in 3rd house. 3rd house and 8th house give longevity to a native. Hence Jupiter gives life not maraka. You have to see the position of Sun. If Sun is in Utthirashada, then he can not give maraka. There are other things to take into consideration for judgement.