Yes. Indeed. But should you?
I was going to say "mix it, I mean" - but at your age even the "can buy" is a little problematic.
I might argue that people can put what they like in whiskey but should be very careful what they put in whisky (by which statement I seek to distinguish between the Scottish kind and most others). Again, much might depend upon whether the Scotch is blended or single malt and, if the latter, whether usual strength or cask strength. Personally, I would only rarely and very selectively drink a blended whisky and never a whiskey of any kind; I also tend to steer clear of cask strength single malts because, in my experience (rather as with certain wines of 14.5%+ alcohol), these often tend to mask their full flavour by reason of their high alcohol content and, in any case, putting anything else in a cask strnegth single malt would risk being a self-defeating exercise.
So - what to put in an ordinary strength (say 40-48%) single malt whisky? Two things only.
One is water, at no more than one part water to two parts whisky - and NEVER put mains tap water into a whisky otherwise it will be ruined thereby (so use either bottled mineral water - preferably Scottish - or water that's been passed through a water filter or, better still, a reverse osmosis unit).
The other is a cheaper option; nothing at all.
Which to go for will be a matter of personal taste and may also vary from whisky to whisky.
By the way, although I currently reside in the West Midlands of England, the nearest vineyard is just 4km distant (although I'd be as wary of sampling what sounds to be their horrible insipid weak white wines as I would be of risking the outlay of some £15 per bottle on their fizz) and the nearest whisky distillery is only around 60km away; no, the former is nowhere near France and the
latter a long way from Scotland but, whilst I've no experience of the products of the former, the latter produces a fine malt that I'd struggle to distinguish from a decent (though admittedly not supremely great) malt Scotch - I refer (generously, as is my wont, of course!) to Penderyn Welsh whisky - well worth a try, look you, boyo...
Best,
Alistair (whose country of origin would not be hard to detect)...