When should kids be given smartphones?
Giving children smartphones at a "ripe" age is a hugely debatable topic, but for the most part it depends on both maturity and trust. It's important for you and your child to discuss the "bad parts" of texting, social media, and the internet as a whole. Sheltering your children will not do them any good in the long run, they'll hide things from you in fear of your judgement. If your family is accepting enough to say "If you're going to drink, just do it around family" your child will have nothing to hide, feels that they can both trust their family, and learns to stay responsible.
I think will have to wait until the children as an adult, because young children self-control ability is poor, easy to indulge in mobile phone, if you want to give it a mobile phone in advance, then I suggest you install mobile phone jammers in the home, prevent them from staying up late watching a mobile phone.
I can't say I would base it off age, but I would base it off maturity. If my kid does well in school and works hard then they would probably get a smart phone at an earlier age. Otherwise if they need a phone than it'll just be a generic flip phone for use in emergencies. No additional things to distract them.