WBWP/Relationship to partner
Indeed, it would be better to specify the nature of your relationship to your partner now rather than have the awkwardness of just treating them as someone who happens to know you and is somehow allowing you to do these things with them. So then, what is your relationship to your partner?
So then, do you want to have one of the more usual relationship dynamics, or do you want it to have a twist to it? I suppose I had best specify what I mean by usual and "with a twist." A parent/child incestuous relationship would be considered normal if the parent was over 18 years older than the child. It would also be considered somewhat normal if the parent was 12 years older than the child as they would be considered a teen parent. However, the "with a twist" category could include the parent being as young as 6 when they had their child who will be their partner for the story.
Please note, parent/child type relationships will not show up as options if you have not put the required number of years difference between yours and your partner's age. Since the default setting for the upper-end of your age is currently "unspecified," all options that would make you your partner's parent will be available.