Using Pega 7.1.9

Consider any flow action. User enters data, we transform this data, and then validate this transformed data. E.g. User enters date of birth, we validate after calculating age. Another example user enters first name and last name. We calculate full name length and throw error if less than some threshold. There are more complex examples which depend on dynamic values such as current time.

I think Pega has severe limitation in this space and this cannot be achieved without a post activity. Declarative rules may be an overkill in many such scenarios.

Pega does validation BEFORE running post-processing data transform and activity. And data transforms cannot validate. Only option is to transform data using data transform and then validate using post activity.

It would be very easy if we could run a data transform after submit but before validation.

Given this limitation, what could be the best/recommended way to achieve this frequent requirement?