I want to gift my boyfriend (24) a perfume/cologne for Xmas. He was obsessed with stronger with you by emporio Armani, but I wanted to get him something that would be a bit more mature and not so overdone, while still respecting his taste.
You could try 
The Most Wanted Parfum
For Designer, maybe the new Hugo Boss Boss Bottled Elixir
More niche - Grand Soir
Not Overdone- By the Fireplace
Given he likes Stronger with You, you can keep it within the same line of sweet and spicy but add a bit of a woody accord to his collection. I'd definitely recommend TF Oud Wood or F*cking Fabulous. Mature, spicy and can spice up a day. 
London for Men Eau de Toilette has some similarities to SWY in my opinion. This is a very rich, Christmassy spicy/sweet scent that is excellent on cold days and very affordable. It feels mature without being stuffy or dated. Check it out!
Oh, so his current scent is something that I would totally avoid, not liking sticky-sweet scents (which might mean we have different tastes). But more mature scents within a similar price range would be, for example: 
Antaeus Eau de Toilette (leather, patchouli, rose), 
Égoïste Eau de Toilette (beautiful sandalwood with rosewood and spices) or 
Dior Homme Intense (2011) (iris, ambrette, cocoa).
But they're all different. Maybe go to a perfumery and check for yourself which one would smell best?
From the ones suggested above, I would definitely recommend London for Men Eau de Toilette . Good and affordable.
If you would like to stretch your budget a little, a spicy scent with a little bit of sweetness coming from oranges is 
Noir Epices .
And btw. I the sweetness may come from different sources. In 
Emporio Armani - Stronger With You , the sweetness comes from vanilla and the praline-like note. Check if you like sweetness coming from iris. A little more sophisticated, maybe. And blends well with spices.
Hope this helps. Good luck!
If you really want something with a bit more maturity,
Fat Electrician would be my suggestion. As I wrote in my review of it, for a good stretch in the beginning, it's very much the more refined older brother of that type of fragrance - and then it dries down to lovely, inviting vetiver. It's the kind of scent that grows up as you wear it.
If that doesn't sound right, though, and you want something a bit more safe/sweet in the same vein, 
Scandal pour Homme or 
Scandal pour Homme Le Parfum would be solid bets, as would 
Invictus Victory Elixir.
Or, if you wanted to scrap the maturity angle, and go full-on sweet and mass-appealling, with a slightly classier edge, you could try 
Le Mâle Elixir - it's not my cup of tea, but people in that age group seem to love it.
EDIT: Oh, you know what? 
Replica - By the Fireplace would be a pretty amazing step up for him, while staying in a similar vein.
Scandal pour Homme Le Parfum, it's like a more mature version of STWY.
Gentleman Givenchy Réserve Privée
Eau des Sens