Hair and makeup is something underlooked directly impacts perceived age and maturity.
I am still told I can pass for a teenager when I don’t wear makeup or do my hair and if dressed casually. Gym, walk, day off etc.
When I have a hair cut styled shorter and blown dry. A touch of bronzer maybe subtle day time eyeshadow and light coating of mascara a tinted lip balm I don’t get the young remarks as much.
Also groomed nails at least buffed shined and cut to a length appropriate for job and upkeep, it is not necessary and can be tacky to polish nails if you aren’t going to maintain. If you go for nail art stay away from loud colors or designs. A french tip or something is simple and elegant.
Accessorize. It makes you look polished though less is usually more. I like to make my pieces practical a sweater if it is cooler, an interesting belt, neat efficient purse, a scarf sure the odd necklace or bracelet. A broach I know sounds old fashioned but can be modern and tasteful actually useful. Of course shoes.
Classic lines, depending on body type, less trendy stuff. Its fun one or two items should do. But it dates too quickly. Well fitting modest. No thongs or tramp stamps showing when you bend over. In fact don’t bend over, but lower at knees legs together back straight.
Posture is helpful it implies a surity and confidence which help translate to age and experience. Yoga stretching and exercise help that. Moving with purpose, noticing and refraining from give aways such as hair twirling, fidgeting, popping knuckles, chewing on lip etc.
A lot of extraneous info, it might be helpful as it could have been something other then clothes that contributed. You probably can identify problem areas and just focus on one at time. I can’t be further help as wardrobe without additional info such as field dress requirements, body type, personal style and coloring as well as climate if you desire something really specific.