JDBC - Prepared statements and PostgreSql Time/Date operations

Hello,

I've got following problem:

I use this simple query:

select * from mytable where creation_time > (CURRENT_TIMESTAMP - interval '7 days');

---> it selects all rows from mytable, which were created before one week or sooner (creation_time is column in mytable).

I would like to use this query in java PreparedStatement, where age of a row would be one of its parameters:

PreparedStatement could look like this:
select * from mytable where creation_time > (CURRENT_TIMESTAMP - ?)

But nothing works with PreparedStatements!
I tried to set whole interval strings "interval '7 days'" as a parameter
I tried to set time strings '7 days' as a parameter
I tried to use BigDecimal as a parameter...

So, my question is: how to dynamically set time interval values to PreparedStatements and how to apply them to my example?
I've searched PostgreSql and Java docs, but i haven't find any cure.

Thanks for help.

JB