What % of the 18-24 age group actually voted remain. I can infer from your stats that 63% of those that voted went remain, however if the turnout in that age group is less than 50% then we could spin it to say only 31% voted remain.
Wrong the turnout for 18-24 years olds was 64%, for the over 65s it was 90% - those are the assumptions I've used.
I have heard of people, as they get older, have a tendency to become more conservative, no idea if this would translate to views with regard to Brexit.
You need to prove that with regard to Brexit - this is an assumption people (wrongly) assume for religion - i.e. that individuals get more religious as they get older. But there is no evidence for this, indeed the reverse seems to be slightly the case. The reason why churches are full of old people is because people born in the 1930s and 1940s always had a way higher level of religiosity than those born in the 1960s or 70s.
And I'm only talking about time-spans of a couple of years - most assumptions about people getting more conservative as they get older is based changes over decades.
Your assumptions (both unsafe):-
1) Turnout remains the same regardless of age
Nope I've factored in differential turnout with age
2) Voting intention remains the regardless of age
Which is of course the safe assumption unless you can prove otherwise. But you are actually rather shooting yourself in the foot, as the demographic shift is on the basis of people dying (and those are most likely to be predominantly the very oldest) and people attaining 18 (who are definitely the youngest voters) - so using your 'get more conservative (i.e.g Brexit) as you get older view would suggest that those dying (and therefore no longer voting) would be biased towards the most Brexit end of the 65+ voting profile, while those attaining 18 would be at the extreme remain end of the 18-24 profile.