Your attraction is normal. How you choose to act, what conclusions you draw about the other person, are the important things in this context.
Sexism would be if your attraction influenced your professional behavior towards your prospective client in any way, negatively or positively.
As you hinted, being able to be less distracted by an attractive figure is a matter of self-mastery, which often comes more easily with maturity, and to some degree familiarity. But a modern gentleman knows to treat others as persons first, not as sexual beings, especially in a professional context.
Sexism would be if your attraction influenced your professional behavior towards your prospective client in any way, negatively or positively.
As you hinted, being able to be less distracted by an attractive figure is a matter of self-mastery, which often comes more easily with maturity, and to some degree familiarity. But a modern gentleman knows to treat others as persons first, not as sexual beings, especially in a professional context.