No, as long as you don't go doing anything stupid like getting pregnant or marrying him. Also be prepared to get your heart broken. He is much older than you and you probably think you're "in love" but really you're not. Just take things slowly.
(28/2) +7=21 => It wouldn't be socially acceptable. To be honest, it's all specific for different people. I'm 25 and wouldn't feel comfortable about dating anyone younger than 22. -Not that I do much dating anyway!