You are saying you aren’t noticing the age difference but maybe she has concerns about it. Are you two planning on marrying or/and having kids? No judgement about age difference but perhaps she thinks about it. When she’ll get 60, you’ll be 80. I am 55 and am “young” 55, id not consider dating 75 year old and certainly wouldn’t consider marriage. Did you discuss with her where is this going and what’s her plans?