Retiring at 48 would have been uncommon, but it wasn't unusual in your mid 50s, particularly for those on final salary pension schemes. Yes, the state pension was 60 for women and 65 for men, but as now, people could retire when they liked, so long as they could fund themselves.
The state pension was relatively lower than now, I think, but so were rents, and more things were free for pensioners, such as dentistry, chiropody and so on, and I think general benefits were more generous, so people could get housing paid for etc. OTOH, people aged faster, as work was generally harder, and people like Ralph and Harry had fought in the war, which would age them. That would make them in their 60s in the 1980s I think - definitely by the mid 90s, which is where we are now in Brookside?
Another thing was that a lot of big employers were offering early retirement and voluntary redundancy to older people. This reduced the numbers on the workforce without adding to the employment figures. Harry and Ralph would have been government employees then, as would the BT chap mentioned above, so would be prime candidates for schemes like that. Harry and his 'dodgy ticker' might have got retirement on grounds of ill-health, too. My father was a civil servant and retired at 55 on full (generous) pension because he was ill. Sadly, he died in 1993 aged 57, so didn't benefit from it for long, but my mum has done well out of it as she retired with him after very few years in work, and still gets her share of his occupational pension as well as inheriting his state one when she was 60.