Loans which are simply - Repayable On Demand - beware of limitation periods

Imagine you helped a family member experiencing financial difficulties and provided them with a loan of $100,000 and let's assume this happened 7 years ago.  Let's say you drew up a simple written agreement at the time to say that the $100,000 was repayable to you 'on request' or 'on demand' or perhaps you didn't bother to confirm the loan in writing at all but had a verbal agreement with your relative that the loan was repayable whenever you asked for it to be repaid.

Fast forward seven years and you now contact the family member and tell them that you need the funds to be repaid, thinking that there would be little difficulty from a strictly legal basis to pursue recovery of the loan. Right? Well this is where limitation periods come into play.