It wasn’t so long ago that 25-year-old Donald Young appeared to be the prodigy who never would arrive. Now he’s becoming something like the guy who won’t go away.

Young made the final of the Delray Beach ATP 250 on Sunday, earning another opportunity to bag the first title of his career in over 10 years as a pro. He was denied in pre-emptive fashion by Ivo Karlovic, a 6-foot-11, 35-year-old Croatian who set a Delray Beach tournament record by firing a grand total of 91 aces last week.

Somehow, the loss seemed emblematic of Young and the travails he’s known. He gets to a final showing wonderful skills and versatility -- and he meets a guy who won’t let him get the ball in play. But Young is like one of those inflatable punching “bop” bags. Knock it down, it pops back up. In Young’s case, the rebound may take a little longer, that’s all.

A decade ago, Young was the world’s No. 1 junior player. (If that doesn’t seem to compute chronologically, the problem isn’t my math; you can blame it on Young’s extraordinary talent, for he was all of 15 at the time.) He was the youngest man to win a Grand Slam junior singles title (Australian Open, 2005), and at the end of that year he became the youngest-ever year-end No. 1 junior, at 16 years, 4 months.

Young also won the Wimbledon boys’ singles title in 2007, at 17. By then, he’d been a professional for nearly three years, leading a strange double life. By day, he was just another struggling young pro trying -- with no great success -- to crack the ATP code in Futures and Challenger events. By night, so to speak, he was the junior champion of the world, ready to take on all comers.

Has any player more convincingly demonstrated that no talent is large enough to guarantee a successful transition from junior to professional tennis?

In 2007, the native of Chicago finally appeared to hit his stride. At 18, the slightly built 6-foot left-hander shaved nearly 400 points off his year-end ranking, finishing for the first time inside the elite top 100 (at No. 98).

But by the end of the following year, he’d slipped 42 notches, and 2009 was even worse; Young nearly fell out of the top 200 (No. 194). Just when many wrote off his long-term prospects, Young regained nearly 70 places in 2010 -- and so on. The curve of his career has been less arc than roller coaster.

There has always been plenty of room for debate on the “What’s wrong with Donald Young?” front, particularly after his stunning rise to No. 39 by the end of 2011 and the crash that followed (12 months later he was back down to No. 190).

True, Young never did develop serious firepower. He’s well on the small side in today’s game and clearly more “tennis player” than buff, all-around athlete. He has marvelous touch, but his finesse and slice-and-dice mentality leave him vulnerable to first-strike attackers.

Some argue that Young turned pro too early and all the one-sided beatings inflicted on him did permanent damage to his confidence. Still others have criticized the continued, dominant role his parents/coaches, Don Sr. and Illona, have played in his life. They have been alternately accused of sheltering, pampering and controlling their son. The Young family’s conflicts with the USTA player development program also are well-documented.

Mostly, though, it seems Donald marches to the tune of a different drummer. That suspicion was planted early.

As a 14-year-old playing in one of his first big junior finals (the U.S. Clay Court 14-and-under Nationals), Young rebounded from the loss of a set to Jesse Levine to win the second set and lead 5-0, 40-15 in the third -- whereupon Levine ran off 23 consecutive points to win the match. That’s the most dramatic, if by no means singular, example of Young’s tendency to lose his focus and mentally check out of a match. In fact, he appears to check out of matches for months running, and that may help explain those peaks-and-valleys on his résumé.

Young’s first shot at an ATP main-tour title came in 2011 at Bangkok, where he was crushed 6-2, 6-0 by No. 4 Andy Murray. On Sunday, ace-maker Karlovic smacked 13 clean ones against Young in a 6-3, 6-3 victory, fending off all seven break points the younger man earned. Young was philosophical in defeat:

"[Karlovic] kind of tosses [the serve] in the same spot, and he can hit all the spots on the court," he said. "You look and see some tendencies. I was able to pick quite a few, but just not when it actually mattered. He played well. He beat me. I didn’t play the best I wanted to play, but all credit to him."

Donald Young was knocked down again Sunday, but lately he’s been bouncing back nicely. He’s off to a good start in 2015 (10-4, with a final and a semi in his last two outings). He’s back up there in the rankings, at No. 45. It sometimes seems as if that first ATP title is just an agonizing inch away -- in a sport where an inch might as well be a mile.