There are different forms of role-play in BDSM. Age-play is one such form: addictive and fiendish. Taking on one or more roles of entirely different age brackets, the most common form being adult baby/diaper lover (ABDL). Even if it's not just about coming together for sex, this form of role-playing can be sheer escapism, a way to let off steam or a means of exploring power dynamics. Really, so long as it's with someone who consents, and doesn't hurt anyone, it's a field where you can let your imagination run away with itself.