Inviting crush to halloween party ?

My best friend is having a halloween party and im going as magenta from rocky horror. When i was talking about it with my mum she suggested that i take my crush (he also likes me btw) as riff raff. the only thing is hes 2 years older than us and i dont think he'd want to hang out with a group of 15 year olds. My mum said she'd ask him for me and she reckons he'd say yes but im not sure if i should or not. My friend would be happy to let him come but it would be so awkward just randomly asking him to go with me when he dosent know my friends and we dont even know each other that well. Should i ask him or not ? please answer!