Yanma doesn't actually evolve at a certain level. Rather, this Pok?mon evolves once it learns the attack Ancient Power. Once that is done, Yanma will evolve the next time it gains a level.
To get Yanma to evolve, it must learn Ancient Power and must gain a level while it knows the attack. Yanma gains Ancient Power as an attack at level 33, so the earliest it will evolve is level 34. The evolved version of Yanma is Yanmega; it retains its bug/flying type. Yanma can be found on both "Pok?mon X" and "Pok?mon Y" at Route 10. There is an equal chance to catch both a male and female version.