There is no minimum age for entitlement to contribution-based jobseeker’s allowance (JSA). However, in practice, because you can only qualify if you satisfy the national insurance contribution conditions, you are unlikely to qualify before you are 18. You cannot claim any type of JSA if you are pension age or over (see here). However, see here if you are getting income-based JSA, you are (or become) a mixed-age couple (ie, you have reached pension age but your partner has not) and you are prevented from claiming universal credit in specified circumstances.