Age difference between husband wife is normal thing but sometimes the gap found so much. Astrology can tell you how much age difference will be there between you and your life partner. How elder or younger your partner will be astrology can tell you.
Astrology can give all answers but some questions have no answers in books or texts perhaps we have to do research of such questions and so many horoscopes we check daily to continue our research which is continue.
The ascendant is of yourself and the very front house of birth chart (horoscope) is of your life partner to whom you will marry or of your husband or wife.
Other than the principal above if the Lord of navamsa is also affected by Saturn the age gap or difference will decreases. If the effect of Mars and Mercury like planets who known very young in astrology the age difference will be more and more. To understand this principal you will need to have intermediate knowledge of astrology. If you want to know the basic thing that is 7th house and lord of 7th house if affected by malefic planets, the age gap between you and your partner will be for sure.