I would date someone much younger than me but I might find it a bit difficult to become fully invested in the relationship, not because I couldn't take him seriously but because I would be carrying a gentle expectation in the back of my mind that eventually he will outgrow this (&me) as his first relationship. Most likely he'll want to explore other options and different lifestyles as he tests his limits and finds himself and wouldn't necessarily consider me to be an ideal partner / long-term outcome for very long. Whereas I know more of who I am and what I want. Like, we may both have goals and ambitions but what those actually are may vary a lot between someone who's 18 (go to college get rich and move to the city) and someone 10+ years older (flexibility, work-life balance, comfort)