I'm with you, OP. Sounds like your dad has no empathy and is a bit of a twat.
I had a colleague who retired and sent postcards to our (frontline, very draining) workplace gloating. I had no desire to be retired at that point but just thought it was mean and tasteless.
I'm closer to retirement now and very conscious that I will retire with my mortgage paid off and a decent - not amazing - pension. Today's young people don't have any guarantee of that at all.
There is a very privileged group of boomers who bought their houses cheap, had multiple cheap foreign holidays, retired (sometimes in their 50s) with good pensions and are now burning fossil fuels spending their pensions flying round the world on endless holidays.
That's not all boomers by any means - there are many living in poverty and there are also young people with plenty of disposable cash. But if you happen to be one of the ones who has the luxury of free time and money to enjoy it, you should be counting your blessings and definitely not rubbing it in the face of someone who is still slogging away and may never get that level of retirement.
And I have resolved never to say "I don't know how I managed to fit work in" after I retire! So galling to people who are trying to fit everything you are doing in your totally free time into whatever is left over after a draining full time week.
The only consolation is that if you are a long way from retirement, you are also - hopefully - a long way from old age and infirmity. The reason so many old people love cruises is that many of them are struggling with minor or major health issues. It is shocking how many friends in their 60s are seriously struggling with mobility. They might not show it to you, but there is a reason why we generally don't work full time in demanding jobs after a certain age. So he can gloat all he likes but you actually have youth and hopefully a long healthy life ahead of you and he will be very aware that he's never getting that back again.