Looks like you were smart without realising it.
In most instances, you will have given your date of birth at application, and therefore the insurer's systems would take that into account when preparing your quote. Premiums are set at the point of the contract beginning, not when you travel.
Alternatively, if you are buying into a bulk policy (with, say a travel agent or operator), the premiums are often clumped together is massive lumps, for example, under 12 or 16 (i.e. child), 12 or 16 to 65 (adult) and over 65 (erm,........ mature person). On those the insurer accepts the collective risk on the basis that almost nobody needs to claim of holiday insurance, and therefore they save on complex systems and up their profitability.
Relax and enjoy your holiday.
The only thing I would suggest you are mindful of is ensuring your insurer is comfortable with your T2. Do you have any application paperwork, or policy wording? You should have (very boring) policy wording at least. The last thing you might need would be an argument over a pre-existing condition, if you needed to claim.