New Quantum Router and ONT

I currently have the MI424WR Rev. F and was thinking of upgrading to the Quantum router, since I would like to extend the signal and take advantage of the AC wireless signal.  My plan is the 75/75, which is fine. 

However, the ONT is obviously about 5 years old.  Will I need a new ONT if I don't plan to upgrade the speed at this time?  I was told if I want to take advantage of upgrading the speed, a new ONT would be necessary.  I don't need to at this moment. 

So, bottom line:  new Quantum router, do I need new outside ONT too?