glmer(prescriptions ~ time + ageBase + hospAdmission + (ageBase|id), data, family=poisson)

glmer.nb(prescriptions ~ time + ageBase + hospAdmission + (ageBase|id), data)

ageCent <- data$agePerYear - round(mean(data$agePerYear))

 glmer(prescriptions ~ time + hospAdmission + (ageCent|id), data, family=poisson)