Don't be the douchebag older boyfriend that your partner is going to regret later on, op.

It's really mostly an issue since, especially if the younger partner is late teens/early twenties, yall have a huge experience gap. Older partners are often in a better financial and experience wise position to push their younger partners into things they aren't ready or willing to do (I. E, marriage, pregnancy, sex acts, etc) and the younger partner might have a harder time saying no or standing firm for their own needs. A 35 year old and a 45 year old are on more or less equal footing since the younger partner is already done with schooling, has almost certainly dated around some, and likely has had a career for a number of years. An 18 year dating a 28 year old likely has no goddamn idea of what they want future wise and likely has very limited relationship experience. Some younger partners are more "mature" but like, obviously, the older partner has their own biased assessment since it benefits them for their partner to be a certain way.