I have always wanted to live by the beach, in a very quiet, specific area, only 10 miles away from where I currently live.
I can probably, just about, afford to buy a house there without selling my current home (would rent it out). However, my son and grandchildren live near where I currently live so I consequently see a lot of them. Also, the area I want to move to is quite remote and has no public transport and no local shop/GP.
I am not yet 60. Yet I have decided that due to the proximity of my family, lack of public transport (for when I'm older and possibly can't drive) and shops/GP, that I have left it too late to move. This is only TEN miles away remember.
Retirement is not the age to make big changes. It's the time to be practical and work out what we might need and want in the next stage of our life.
You'll want to regularly see your grandchildren. You won't be able to. Your relationship with your children will suffer. It will be VERY hard to move back to the UK when you're older. House prices will have left you behind and the organisation of it as an elderly person (rather than a recent retiree) will need you to rely on the children.
I've lived overseas a lot, in several different countries. Living there is very very different to holidaying there. Many European cultures are very insular and don't take well to Brits abroad (holiday makers are OK). It can be very isolating, unless you live in a British enclave overseas.
The very time I wouldn't want to move overseas would be in retirement. A holiday property maybe, but retaining a UK base. Never a permanent move. I can't imagine trying to deal with Spanish bureaucracy without an employer to try to guide me through that treacle!