I see both Jasmine and Alexa as insanely smart girls who are both fun, playful, and mischievous but I don't think I'd call either of them immature. They tease the MC in a playful way, but I don't think either of them have really shown any emotional immaturity or lack of respect for Jake.
What I would consider immature is a girl who slides the "girlfriend" talk into conversation even after her FWB (of 2~3 months) has said he's not ready for a relationship yet... and then gets so upset by when he doesn't take her to the Ball that she fucks off to Canada. I think that would be pretty immature.