For many people, being on the far side of 40 in the workplace brings the confidence of experience, of having hit a certain professional stride.

It can also bring a nagging insecure feeling that younger colleagues -- the ones with 5,000 Twitter followers, who designed their first website in middle school -- are fast becoming the new office stars.

Doug Gould, a 50-year-old advertising veteran, says some of that anxiety arose when co-workers called him by nicknames like 'Uncle Doug' and 'Coach.'

'I think those were terms of endearment,' says Mr. Gould, a creativedirector for the Boston ad agency Allen & Gerritsen, who started his career back in 1984 using tracing paper and markers to design newspaper ads. 'But if you read between the lines, it also meant 'old guy.' I get nervous about what that means.'

For many people in the back half of their careers, the meaning is becoming all too clear: To keep from drifting, or being nudged, into an early retirement, it's time to add more high-tech arrows to their professionalquiver -- to refresh their skills with, say, some social-media or mobile-app expertise. As Mr. Gould has learned, competing with younger colleagues who grew up texting, tweeting, using Facebook and playing videogames requires constant work to stay up-to-date.

Even with an impressive resume filled with more than a dozen industry awards -- and two memorable Super Bowl ads -- Mr. Gould knows he can't rest on his laurels. 'Fifteen years ago, I thought I knew everything,' says the husband and father of two teenagers who says he intends to work another 15 years or so. Now, 'there is new technology out there I don't know the first thing about, that could easily turn me into a dinosaur if I don't continue to adapt.'

In the past few years, he has taken more than 10 new-technology courses, both online and at a professional training center -- from a seminar in the location-based social network Foursquare to a recent class in Adobe Muse, which lets him design and publish HTML websites without writing code. He now also tweets and blogs.

Rather than leaving hands-on work to underlings, as many executives do at his stage, he continues to use new design and animation programs to generatecreative products like print, digital and broadcast ads and websites. 'If I become a manager and nobody wants a manager, how am I going to thrive in my later years?' he says. 'The lifeboat for me is to be able to still do the work.'

He also looks for new challenges. He worked for a decade at a big agency, Hill Holliday, and was comfortable there. But he left two years ago to take a similar title at Allen & Gerritsen because he wanted a chance to help a midsize agency grow. 'That was something I hadn't done before. I saw this as a challenge,' he says.

Older workers have accumulated knowledge that is hard to replace, research shows. But lagging tech skills are one reason job-loss rates for experienced older workers 55 and over have exceeded those for younger workers by a growing margin for the past decade, Bureau of Labor Statistics data show.

Mr. Gould worries about surviving in a field where most of his counterparts are in their 30s or 40s. While he was quick in his late 20s to embrace new computer graphics programs that made hand drawings obsolete, he saw many older colleagues fall by the wayside. 'Some of them didn't want to learn, or were afraid to learn,' he says. 'I thought, 'I hope this will never happen to me.' '

When social media and digital technology turned advertisingupside down again many years later, Mr. Gould says, 'I looked in the mirror and said, 'Oh my god, it's possible that I could become that person who fails to keep up.' '

Mr. Gould resisted using Twitter at first. 'I said, 'You're kidding me -- 140 characters? That's it? The whole world is moving to phrases?' '

But after coming to see it as an efficient way to share information -- instead of a truncated form of personal communication -- he made Twitter the basis last fall of a campaign for the nonprofit City Year, #makebetterhappen, which has drawn more than 20,000 tweets from volunteers telling upbeat stories from the classroom.

Gillian Smith, City Year's chief marketing officer, says Mr. Gould's 'great creative work' sparked a 37% year-over-year increase in City Year's website traffic.

Mr. Gould also tries to learn from younger colleagues. Ben Daly, 33, an associatecreativedirector at Allen & Gerritsen who specializes in digital art and design, says Mr. Gould sat with him about two years ago and asked him to explain changes he was making in the agency's website so it would function well on tablets and phones as well as on computers. Mr. Daly says Mr. Gould quickly saw the technology's potential for their clients' sites as well. Allen & Gerritsen has a reverse-mentoring policy to encourage such exchanges.

Of course, the help can go both ways. According to Mr. Gould, 'somebody like me can teach people who are so ridiculously tech savvy how to handle themselves in a meeting when things go wrong.' Mr. Daly says Mr. Gould sometimes coaches younger co-workers during client presentations, stepping in to help them over rough patches, without stealing the show.

While he has successfully leveraged social media in specific projects, he isn't as immersed in it as many younger professionals. Mr. Gould follows 158 feeds on Twitter, from the Harvard Business Review to the Onion, but only tweets occasionally to his 180 followers. 'I tweet when I feel like I have something to say,' he says. He blogs occasionally on Tumblr about politics, sports or personal topics. Twice a day he checks Facebook, where he has 517 friends.

He is selective in his social-media use, bypassing Foursquare and the social-network Google Plus, for example. 'There's pressure these days to get into everything, but you have to stop yourself,' he says.

In the evening, he turns everything off when he goes home. 'I don't believe you can listen to your kids when you're staring at a screen,' he says. He always tries to have dinner with his family, and he has breakfast with 17-year-old daughter Abby, a high-school senior. His wife of 22 years, Julie, 49, runs a custom window-treatment business from home. He talks by phone weekly with their 19-year-old son, Davis, a sophomore at West Virginia University.

Those boundaries come with a cost. Mr. Gould worries when he sees new hires walk in the door knowing technology he hasn't learned. 'You're working 50 hours a week, through lunch, and when you go home you're trying to raise a family. And you see the company hiring these new people who just spent four years in college learning to do what you can't do, that you have no time for,' he says.

'The speed of change makes you uncomfortable on a regular basis,' he says. 'That's so difficult for people who are paying mortgages, buying cars, trying to give their kids the things they had, to get them through school. You want to feel confident in the last 15 years of your career that after 25 or 30 years of effort, it's just going to work,' he says. 'But it isn't so. And I don't think you ever get over the fear of not knowing.'