I have given this a lot of thought Kiora and think there are several things to take into account
1) Finances - as the others have said, go into it with yur eyes open. Like Mishap I restarted my career and my pension is based on 22 years instead of the 35-7 most teachers enjoy. Frankly money is tight also because of DH's extended periods of ill health and no earnings (he went self employed after reduncdancy 20 years ago - not ideal given the subsequent medical problems) It didnt seem to matter so much while I was working but I am conscious of friends enjoying a variety of holidays, cruises, home improvements or buy to let purchases and while we are far from the breadline, it is a shame to have all this time at our disposal, but in our case neither the finances or health to do likewise. Not complaining, just be aware
2) your current fatigue might not be (just) age-related - do have a health check. I felt great uo to 60/61/62 and contemplated part time to "ease myself" into retirement, but circumstances dictated otherwise (DH's illness and first DGS) so I just quit at 62. So do see a doctor.You may be suffering from depression or be anaemic or something else.
3) it depends how much you enjoy your job. I could have bored for Britain about mine and loved it right up to my 62nd birthday when either because I knew I was going or because I was weary, I totally fell out of love with it and that's no way to go out to work!
4) Everybody will tell you how wonderful retirement is- one long holiday, no more Monday mornings, live for yourself, etc etc. You may find it harder to adjust than you think. On the one hand you free but you are also available for help with the DGC which can be lovely, or for your own parents, or for your partner - remember to leave time for yourself or you risk exchanging one tyranny for another! Many people if they are being honest will admit that it isnt always a bed of roses, you may miss the company or stimulus of work, the identity it gives you and the feeling of being significant.
I am sorry to sound depressing, it just isn't necessarily as easy as it might sound. I think the main thing first is to see a doctor and explain how you feel and onky after that, plan your next steps. Just because you are 60 shuld not make you unfit for work!! Good luck.