I'd second the half plus seven @Wattersun mentioned. Age old rule of thumb that keeps the creep factor out. Perfectly plausible that a 35 year old and a 25 year old have common interests and are in a close enough station in life to build together. By the time the "plus seven" allows for an age gap where that becomes fairly implausible everyone has enough life experience that they should know what they're signing up for. E.g. an early twenties dating a late thirties might be naïve enough to not think of long term consequences of age gap and think "it'll just work it out." Compare, say, a 32 year old dating a 50 year old. While the age difference is the same as the early 20s / late 30s match, and realistically they're equally in different stations in life, the 32 year old should know what the deal is. Pretty much why when most see a 40 some dating a 20 some the common negative judgement is, "That creep is cradle robbing." But if you see 50 some dating a 30 some the default negative judgement flips to more like, "Looks like someone is a gold digger."