Optimum or optimal

Is there a difference between optimum and optimal?
As adjectives, they have the same meaning: best; most favourable; most conducive to a good result
They both come from the Latin optimus, meaning “best”.
Look at these examples:

• What is the optimum/optimal childbearing age?
• We need to find the optimal/optimum solution.
• In our case, the optimum/optimal investment would produce a modest return at no risk.

Optimum can also be a noun, while optimal has two derivatives:

• optimally (adverb)
• optimality (noun)