You can use a serum containing vitamin C and providing it is well formulated, it shouldn’t do you any harm. But as with anyone at any age, I would query why you think it’s necessary and suggest that there may be a simpler, less expensive way to go.
Vitamin C, applied to the skin in a serum or moisturiser, is usually chosen by people wanting to repair damage. This tends to be reduction of pigmentation in marks on the skin as a result of sun-damage, to boost collagen and elastin synthesis and as an antioxidant. It has the most beneficial effect where there is an existing vitamin C deficiency (in the body).
If you have scars, from inflammation or infection in the skin, for instance, acne, then vitamin C could help to fade this. It will work as an anti-oxidant on any skin, it doesn’t differential between mature and young skin! So if you live in a urban environment or somewhere that air pollution is a concern, using vitamin C in a topical treatment could also increase the protection from this. (You need to find a product that is either formulated not to oxidise quickly or in a container that reduces the rate at which it oxidises - preferably both - otherwise it won’t help.
It can irritate, especially if it is in a product at over 5% or if it has oxidised significantly. It can be expensive and there may be cheaper alternatives for the skin problems you are seeking to alleviate. If you believe that your diet may be lacking vitamin C, you can address this by increasing the amount of fruit and vegetables you eat, or if that is difficult, supplements are available - again, you don’t need mega-doses, the recommended daily. A sun cream with broad spectrum protection will help the skin to preserve the plentiful amounts of collagen and elastin you probably still have.
As with anyone of any age, you should know why you are buying a product with a particular ‘active’ ingredient. It is likely to be more expensive than one without and you may not need it. It is commendable to be thinking sensibly about skin condition, protection and health at your age, but try to avoid being lulled by clever marketing to buy something that will make little difference.
After protecting your skin in hot sunshine, a light lotion containing hyaluronic acid or simply vegetable glycerine, aloe vera, and a nice light butter should keep your well skin hydrated. Make sure you keep it clean, so remove any daily dirt or makeup with a hydrosol or light cleanser (not soap unless it is specifically formulated for this and so has a pH lower than 6) and enjoy your wrinkle-free years!