If I were taller, I would not buy those heels.
Based on this sentence we cannot deduce:
(a) How tall the person is, or whether or not they may become taller in the future. The person may be tall or short, and they may still be growing or they may have already stopped growing. 'If I were taller' is purely a hypothetical statement, it does not imply that the person will or will not grow taller.
(b) Whether or not the person has already purchased the heels. However, it is likely that they have not yet bought them, because if they had done so then they are more likely to have said, 'If I were taller, I would not have bought those heels.'
From this sentence we can deduce that the speaker thinks that the heels would not be suitable for them if they were taller than their current height.