The gate has dropped. You can see it from the kitchen window: the bottom corner now drags a groove in the grass, and the latch no longer meets the catch without a shove. Your father has said it is fine. He has also been walking around the gap for a while, which tells you it is not fine. This is the decision in front of you: fix the hinges yourself on a free morning, or call a carpenter.
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Look at the post before the hinges
Most sagging gates are a hinge problem, not a gate problem, but you have to rule out the post first. Push the gate up and down at the latch side and watch whether the post moves. Grab the post near the top and rock it. If it wobbles, the fault is in the ground or in the post, and new hinges will sag again. Tap the base of the post with the handle of a hammer. A solid sound is good. A soft, hollow sound often means rot at the ground line.
Check what is loose
Look at the screws in each hinge. If the heads are chewed up or the holes look bigger than the screws, the wood has stripped. Stripped holes can often be rescued by swapping in longer exterior screws that bite into the post and the gate frame, or by packing the hole with glued wood dowel, letting it cure, and drilling a new pilot hole. If the screws still spin after that, the wood has given up and you need a different answer.
Decide: yourself or a carpenter
Do it yourself if the post is solid, the gate frame is square, and the only problem is loose or stripped hinges. You will need a drill with a driver bit, exterior screws, a level, and a second person for the first lift. Prop the gate on a scrap block under it so the weight is off the hinges while you drive the screws.
Call a carpenter if the post rocks, the gate frame has cracked corners, or the gate is too heavy for one person to lift cleanly. Also call if the gate is part of a longer fence that is leaning, because a single gate repair will not hold a fence that is moving. When you call, ask whether the quote covers replacing the post or only the gate, whether the carpenter carries liability insurance, and whether materials and any second visit are included.
What to do tonight
Walk out with a level and a flashlight. Mark whether the gate sags at the latch side or the hinge side. Tighten every visible screw, but do not force a loose one through wood that has already given up. Your father will want to inspect the work afterward. Let him. He knows where the level goes, and he will tell you so.
When to get someone out
Call sooner rather than later if the gate pulls away from the latch, if the post leans toward the house, or if there is a gap wide enough for a child or a dog to slip through a gate that is meant to keep them in. A gate that swings on its own is a hazard, not a chore.